Brian,

here is all about your gunsight, maybe of interest for other oldies.

/Inge



The Reflector Sight 

In 1900, the noted scientist and optical instrument designer, Sir Howard
Grubb (1844-1931), filed Patent No.12108 for 'Improvements for sighting
devices for guns'. In the following year the Royal Dublin Society
published a paper by Sir Howard entitled 'A New Collimating Telescopic
Gunsight for Large or Small Ordnance'. 

The basic principle of the reflector sight is as follows: 

In the base of an upright tubular housing there is a light source. This
is directed through an opaque glass plate on which is etched an aiming
mark, or graticule. The image of the graticule is projected through the
focal plane of a collimated lens, and reflected onto a glass screen
mounted 45 degrees to the gunner's eye. This presents an aiming mark,
usually a ring with a central dot on the reflector screen, giving the
gunner a clear view of the target with the graticule pattern
superimposed on it. 

Sir Howard's first design used natural light reflected by mirrors, but
after trials these were replaced by an electric bulb (such illumination
was mentioned in the original patent). He approached various arms
producers, including Vickers, but although they were impressed with the
performance of the sight, no orders came. Ironically, this first sight
was invented before the Wright brothers left the ground. 

In 1915, Vickers decided to develop a reflector sight with Sir Howard as
consultant. Although a patent was applied for stating that the sight
would be useful against aircraft, no mention was made of possible
aircraft use. 

The Oigee sight 

The first record of a reflector sight, being used on aircraft was in
Germany, where in 1918 the optical firm of Optische Antal Oigee of
Berlin, working from the Grubb patents, produced two reflector sights
for aircraft. One of these was fitted with a sun screen, and could be
used by day and night. A smaller version was meant for night use only. A
small electric bulb was used as a light source, the reflector being an
elliptical glass screen. The sight could be harmonised with the gun by
means of a screw and clamp. 

Several of the larger version were issued to Jasta 12 in 1918, when they
were fitted to Fokker Dr.1 aircraft for operational trials. Others were
tested on Albatros D.Va aircraft. In 1920 the US Military Attache in
Germany was given a demonstration of the sight. He was so impressed that
he sent an example to the US Army Engineering Division at McCook Field,
but no official interest was shown.



After Grubb's work and the designs of other manufacturers had been
studied, an experimental pilot's sight was produced. It consisted of a
horizontal lens tube mounted under a rectangular Triplex reflector.
Light from a bulb was directed through a circular pattern stamped out of
a metal disc, and a collimated lens train to a prism, which turned the
image 90 degrees up onto the reflector, which was fixed at 45 degrees to
the pilot's eye line. A twin-filament bulb was used to vary the
brightness. 

The prototype sight, known as the Barr & Stroud GD1, was despatched to
Martlesham Heath where it was tested on an Avro 504. The trials pilot
reported that the graticule was not clear enough against white cloud,
even with the smoked-glass sun screen in position, and the optics misted
up after flying through cloud. The sight was completely redesigned in a
new configuration, with the lamp at the base of an upright tube, the
graticule being projected straight through the lenses onto the reflector
screen, and heat from the lamp prevented misting. The lamp strength was
increased, and a modifed dimming screen was raised in position by a
knurled knob. This design, the GD2B, received favourable comments from
the trials unit in 1927. Work then started on a sight for free-mounted
guns. 

The ENI sight 

In 1931 the German Oigee company produced another reflector sight, the
ENI (Electrische Nivellier Instrument, or Electrical Levelling
Instrument). Germany was forbidden to produce armaments at this time, so
the company used this acronym to promote sales. Again, Lt. Col. Jacob
West, the US Air Attache, sent an example to McCook Field, where it was
tested by the 17th Pursuit Group on Boeing P-12F aircraft. As a result,
the Armament Laboratory at Wright Field designed an American version, an
L-shaped housing in which a central cross graticule was surrounded by
eight small arrows to assist sighting. This was the forerunner of the
American 'N' series used by the US forces for the next 20 years.



The GD5 

In 1934 a new Barr & Stroud sight was announced. The GD5 was a complete
departure from previous designs. The sight consisted of a lens tube
mounted in the centre of a 114 mm (4.5 in) bowl containing a parabolic
mirror. The principle of the sight was to separate range-finding and the
aiming graticule. The upright tube contained a collimating lens which
projected a cross graticule. The parabolic mirror reflected a circular
ranging ring which was adjustable to various diameters representing
various wingspans. The system used a single bulb light source, and the
images were projected up onto the pilot's windscreen. The ideal eye
point was given as 419 mm (16.5 in) from the sight, giving an angular
field of 7 degrees 40 and allowing eye movement of 25.4 mm (1 in) either
side of the centre of the windscreen. 

The GD5 was specifically designed for use in the new Hawker fighter, the
Demon. The prototype was tested at Martlesham on the prototype demon by
a pilot who made a rough landing and was struck in the face by the
protruding sight. This was to be a common hazard with reflector sights.
Thick rubber pads were later fitted to the rear of the housing, but the
problem was never fully overcome. 

Accuracy of the new sight left much to be desired, and it needed
continual realignment. The main problem, was double imaging of the
graticules, caused by the Triplex glass of the windscreen. It proved
difficult to produce surfaces sufficiently parallel to avoid this fault.
As the sight had been designed from the outset to use the windscreen as
the reflector, it would have needed a complete redesign to adapt it to
an integral reflector. Meanwhile, squadron Demons were fitted with the
usual Aldis and ring sights. 

Later in the year the company was asked to provide a reflector sight for
the PV3, which was to be the last of the famous line of Hawker biplane
fighters designed by Sydney Camm. The Barr & Stroud drawing for the new
sight, the GD12, specified its use in the Hawker Hawk. It was virtually
identical to the GD5. It would appear that the company, realising that a
firm order would be unlikely, had submitted a design as requested, but
also mentioned that a completely new pilot's sight was being developed
which would be more robust and less complicated than the GD5 series.



Free Gun Reflector Sights 

The first sight designed by Barr & Stroud for free-mounted guns was the
Type J1 of 1926. This was fixed on a bracket clamped half-way up the
barrel of a Lewis gun. A circular reflector screen was mounted over a
cone-shaped lens housing, with a sun screen which could be raised into
position at the rear. Although the sight was well elevated above the
barrel, the need to clear the ammunition drum put the gunner's eye
position too distant for easy sighting. Its position hard on the barrel
also ensured short bulb life. However, the new sight was found to be
accurate when it was tested at Farnborough, where several improvements
were suggested before it could be considered for Service use. 

After the J1 was evaluated at Farnborough it was decided to change the
format. The new design consisted of a rectangular lamp housing which was
offset from the gun centre line. A bulb projected a ring graticule from
the side of the housing onto a prism, which directed the image through a
lens system onto a small circular reflector screen behind which was a
swing-in smoked-glass sun screen. To be known as the GH6, the sight was
fixed on the side of the gun clear of the drum, with the sight head
protruding from the side to a position in line with the gunner's eye.
The GH6 was found to be effective and was accepted for small-scale
trials while an automatic 'own speed' and deflection system was devised
on the lines of the Scarff compensating mount. This consisted of a
pillar on which were speed settings, the sight being fixed to an arm
fitted at right angles from the top of the pillar which varied the line
of sight according to the setting. This required deft manipulation of
the adjusting knobs, not easily accomplished with heavily gloved hands.
The compensating mounting received the title Type GH2 No.14, but was
never issued for Service use.



The Mk 1 Free Gun Reflector Sight

The GH6 was used by gunners of a flight of Handley Page Heyfords taking
part in the 1934 exercises. During a night attack on a 'blue-land' city,
searchlights picked out the 'raiders' and the gunners reported that the
beams had caused dazzle on the reflector screens (there were also
reports of sunlight having the same effect). After various experiments,
it was found that a small hood over the reflector prevented most of the
dazzle and also protected the screen from damage. This feature was
incorporated in a new sight, the Mk 1 free gun sight, which had similar
optics to those of the GH6 but was much more compact and practical. The
lamp housing and rheostat was a separate unit, quickly detached for bulb
changing. Like the GH6, a prism projected the graticule onto a hooded
screen, offset from the sight body above the centre line of the gun
barrel. The double-filament lamp could be dimmed from full brightness to
extra low to suit conditions. The diameter of the bright orange
graticule represented the deflection for a target crossing 80 km/h (50
mph). The graticule, the could also be used as a range-finding aid: if
the span of a twin-engined fighter filled the graticule, the range would
be 274 m (300 yds); if it filled the radius it would be 549 m (600 yds).
Barr & Stroud then decided to develop a turret system using the same
features, but without the prismatic sight. 

The GJ3 - Pt 1 

As bomber speeds increased in the 1930s, windscreens were fitted to
protect gunners. The next step was to enclose the gunner in a glazed
cupola which could rotate. Some manufacturers then decided to develop
enclosed, power-operated turrets, with the guns remote from the gunner's
eye line. It followed that the sight also had to be remote from the
guns, but linked to the gun movement. Barr & Stroud's answer was the
GJ3, which, when fully developed, was to be produced in larger numbers
than any other British sight. It consisted of a detachable lamp unit and
an upright sight head, the glass reflector screen being fitted to a
housing surmounting the lens tube. The reflector housing supported a
swing-in-type sun screen operated by a small knob at the side.



The GJ3 - Pt 2

The prototype sight was tested at the weapons department at Farnborough,
where the optical system and electrics were proved to be satisfactory.
It was then sent to Martlesham Heath, where it was installed in a
Parnall Hendy Heck fitted with two Browning guns, and air firing trials
were carried out at various heights and at ground targets. The trials
reports were favourable, although it was recommended that a protective
hood similar to the Mk 1's should be fitted. It was decided to fit the
reflector screen into a slot fixed to the inside of the hood, and
incorporate the sun screen at the rear operated by a knurled knob. The
sight head could be adjusted for elevation, and it was clamped onto the
lens tube, giving a means of lateral adjustment. The sight was
reassessed and found, in the words of the official report, to be 'an
accurate and compact sighting medium suitable for use in powered
turrets, and situations where the Mk II* would not be ideal'. The
company was given a production order for an initial batch, the sight
being given the Service title Mark III Free Gun Reflector Sight.



The GJ3 - Pt 3

When production got under way, the company's lens-making department was
fully extended, the Mk III and Mk II pilot's sight (described later)
requiring many high-quality lenses. As demand increased, sub-contractors
were appointed for some of the work. The Glasgow team then decided to
produce a version of the Mk III with stadiametric ranging, but it was
found to be difficult to operate with heavy flying gloves. 

The Mk III series proved to be one of the most successful reflector
sights ever produced. Virtually every turret in RAF Bomber Command used
it, and it was adopted by the USAAF and US Navy as the Mark 9, produced
in America by the Woolensak Optical Co. of Rochester, NY, and in
Australia, by the Kriesler (Australasia) Pty Ltd. (This model featured
an anti-vibration lampholder). As well as turret use, it was fitted to
free-mounted Vickers K guns, and, being less obtrusive than the Mk II*,
was used as a pilot's sight on many multi-engined aircraft. The final
redesign was the incorporation of a tilting head mechanism for rocket
firing. 

The production versions were: 

Mk III: First version, no in-built adjustment, 24/12 v 
Mk IIIA: Die-cast, modified adjustment 24 v, short hood 
Mk IIIA*: Main production version, some bakelite housing, 24 v 
Mk IIIG: Tilting head for rocket firing use 
Mk IIIL: Tilting head with hood 
Mk IIIN: Hood deleted 
Australian Mk III: Spring-damped bulbholder 
US Mk 9: With or without adjustable head 

In most turrets the sight was mounted at the gunner's eye level and
connected in elevation to the gun cradle by rods and cranks (in rotation
the sight moved with the turret). Nash & Thompson FN4 tail turret
gunners often used the sight as a convenient handhold when getting into
their seats, which could put the sight out of alignment, so a prominent
'Hands Off' sign was attached



Hawker's sight bar

Before the adoption of the new Barr & Stroud fixed gunsight, weapon
aiming remained traditional. Hawkers fitted a long sight bar for the
ring and bead on which the pilot could choose the position of the two
elements, some preferring the the ring in the centre with a bead at
either end. Although the Aldis was more accurate, some pilots preferred
the ring and bead, especially during fast manoeuvres when 'g' forces
made it difficult to align the small eyepiece. Another reason was that,
when engaged in low-level air-to-ground firing, the pilot needed full
peripheral vision to avoid flying into the ground. The Aldis also
restricted the field of view at a time when targets of opportunity could
appear. Another advantage of the 'iron sight' was that when engaging
ground targets, the point of aim was in front of the impact point, and
it was not easy to do this with the Aldis. 

Prismatic Sights - Pt 1 

The reflector sight was not universally accepted as ideal: during trials
at Northolt and Farnborough, pilots complained that the graticule was
hard to see against bright cloud, and could not be held in view in a
tight turn. These complaints were usually made by older pilots used to
the black outline of the ring and bead, and as they were of a higher
rank, a conference was held at Farnborough on 12 October 1938 to discss
alternative systems. The Armament Department of the Royal Aircraft
Establishment suggested a sight similar to the Aldis, but using prisms
to reduce the size for use behind the windscreen. The RAE were given an
order for two such sights, the GI type 'A' pilot's sight, and the type
'B' for free guns and turrets. These were to have a black-line graticule
and a facility for night illumination.



Prismatic Sights - Pt 2

Messrs Ross Ltd produced four type 'A' sights, to be given comparative
tests with reflector sights in a Gloster Gladiator. The type 'B' was
produced for use in turrets, but the small 20 mm (0.78 in) eyepiece
proved a drawback, and it was soon replaced by the Mk III reflector
sight. All work on prismatic sights was finally abandoned in 1940. The
G1 was used as the optical head of the Mk 1 Gyro, and some Bristol B.1
turrets used it, but from 1940 onwards the reflector sight became
standard apart from the ring and bead sights used on some free-mounted
guns, as mentioned elsewere.



Barr & Stroud GM Series Fixed Gun Sights

Although the GD5 pilot's sight had proved to be quite effective, the
windscreen projection system had caused problems with double imaging,
and it had proved difficult to manufacture. With this in mind, the
company was asked to design a sight with an intregal reflector which
would be more suitable for series production. In late 1935 the prototype
of the new sight was submitted for evaluation. The optical department
produced a lens with a numerical aperture of F/O=.68, through which a
large circular graticule was projected onto a circular glass reflector
screen 76 mm (3 in) in diameter. The graticule was bisected by a cross,
the horizontal bar of which was broken in the centre, the gap being set
by (1) a knurled ring which turned a perspex pointer to various range
settings, and (2) an adjustable ring which turned an indicator to
wingspan in feet. The internal mechanism then set the gap according to
the required range. A central dot was added for a further aiming point.
The pilot first set the span dial to the known wingspan of his
prospective target, then the range dial to the maximum for accurate
fire. When the target coincided with the gap it was within range. The
radius of the graticule ring gave the deflection allowance for hitting a
target crossing at 161 km/h (100 mph). The sight, designated the GM1,
was illuminated by a half-silvered 12v lamp in a quick release holder at
the base of the sight body. 

The prototype was tested at Farnborough, and then at Martlesham in a
Bristol Bulldog for air firing tests. The trials reports led to various
modifications. A substantial rubber pad was fitted to protect the pilot
from injury in the event of a rough landing, the range/base setting was
modified to two similar knurled rings with their own scale and
indicator, and the lamp changing was also made easier. The blue-tinted
swing-in sun screen was found to be effective in high brightness
situations although the orange graticule was not perfect in some
conditions. The modified sight was designated the Barr & Stroud Type
GM2, and was accepted as the standard fixed gunsight of the RAF, being
known as the Reflector Sight Mark II. it was patented in 1937, and the
first sights of an initial order of 1,600 reached aome Gloster Gladiator
squadrons in 1938.



At the time of the Munich crisis in 1938, increased orders were placed
for the Mk II for the new Sptifire and Hurricane fighters just coming
into production. Even with 24-hour working, Barr & Stroud were already
at full strech, and as all British companies with the required
production facilities were committed to other defence contracts, the Air
Staff asked the company to find an overseas licensee. This resulted in
an agreement being signed with C.P. Goerz of Vienna. Drawings and a Mk
II sight were sent to Vienna, and Herr Neumann of Goerz concluded a
produciton contract with an Air Ministry representative. In early 1939,
with 55 sights delivered, the Anchluss was signed between Germany and
Austria. However, Air Ministry fears of cancellation were groundless and
Goerz were only too pleased to honour the contract, 700 sights known as
the GM2 Mk III being delivered before the outbreak of war in September.
These gunsights made by the 'enemy' were invaluable, as production at
Glasgow could not satisfy the needs of Fighter Command. In early 1940
the situation was eased when the Salford Electrical Co. began production
under licence. The sight was used in most British fighters of 1938-43,
although as mentioned earlier, some Beaufighters and Mosquitos used the
Mk III* turret sight for fixed guns. 

The first change in the design was made in 1941. when the circular
reflector glass was replaced by one 114 mm (4.5 in) square, the circular
design having been found to have slight optical aberrations. This
modification was designated Mk IIs, later Mk II*, fixed gun reflector
sight. Existing sights were retrofitted with new sights heads, and the
circular sight heads are now highly prized by collectors. The dimming
screen was discontinued, as it was said to be rarely used. 

When rockets came into widespread use, a special version of the GN2 was
designed in co-operation with Farnborough, to allow for the increased
gravity drop of these projectiles. The reflector screen was made to tilt
forward by the pilot from 0 to 5 degrees depression, according to
airspeed and the known drop of the missile being used. This
modification, which involved the replacement of the sight head, became
known as the type 1 Mk II conversion, and the sight then became the Mk
IIL.



The Beamont Modification

S/Ldr. R.P. Beamont commanded a squadron of Hawker Typhoons engaged in
low-level attacks on German installations in occupied France. Low clouds
and poor visibility were often encountered, and it was found that, even
if the gunsight lamp was turned right down, the large ring and range bar
tended to obscure tracking and target aquisition. Beamont decided to cut
down the graticule pattern on his Mk II* sight, so squadron armourers
blanked off the ring and bars, leaving only the centre dot visible. The
smaller aiming ring proved a big success: Beamont could discern much
more without the large orange glow. 

On subsequent operations he realised that it would be even better if the
glass reflector screen was removed and the graticule projected onto the
windscreen, the rake of which was 45 degrees. The following day he used
the sight in an attack on an installation in the Lille area, and found
he had a better field of view than ever before, so he had all No.609
squadron's sights altered to the same configuration. When news of this
modification reached the authorities, terse instructions were issued to
remove the unauthorised alterations forthwith. Eventually it was agreed
that in low light conditions the system had its advantages, and the spot
was easily seen in full daylight conditions if the brightness was fully
turned up. 

Type I Mk III Projector Sight 

Beamont's modification was taken up by Farnborough and a new version of
the Mk II* sight was designed with the reflector screen removed and the
graticule modified to a plain 161 km/h (100 mph) ring and dot. The two
control rings were replaced by a single ring which moved the graticule
forwards or backwards, raising or lowering it on the windscreen. A
dual-purpose graticule was devised consisting of an adjustable ring for
rocket-firing and a dot for the guns. An angle of depression scale was
fitted, but it was found that a white celluloid strip, on which a pilot
marked settings for various dive angles with a marker, was more
practical. A detachable shroud was fitted over the sight head to prevent
images of the sun being reflected into the pilot's eyes. 

Trials revealed several shortcomings in this model, which was known as
the Type 1 Mk III projector sight: the graticule was dim and allowed
very little eye movement. However, a simpler modification was agreed in
which the graticule reverted to a single dot only, without a reflector
glass. A production order was issued for this version, which was first
officially used when the Hawker Tempest Mk V entered service in February
1944. Similarly altered Mk IIs were also used by night-fighter and
Typhoon squadrons. Beaumont's modification was further improved when
Grade A armoured windscreens became available. These were optically
correct, and prevented the double image which sometimes occurred if the
lamp was turned up to high (shades of the GM5). In a special
night-fighter version tested by the Fighter Interception Unit in
November 1942, a green filter diffuser cell was inserted between the
lamp and the graticule to enable tracer to be seen to a maximum range at
night. Another idea tested by the Air Fighting Development Unit
consisted of an optically correct reflector glass screen the same size
as the windscreen fitted 38 mm (1.5 in) behind it, which gave the pilot
much more eye movement. 

More than 84,000 GM2 sights were manufactured, mostly by Barr & Stroud,
the production of lenses alone amounting to over 1 million units. The
production versions were as follows: 

Mark II: Oval reflector with sun screen 
Mark IIs: Rectangular reflector with no sun screen 
Mark II*: Similar to the IIs, slightly different dimensions 
Mark IIL: Adjustable sight head (0-5 degrees) for rocket firing and 40
mm guns 
Mark III: Produced by Goerz 
Type 1: Mark 1 (Projector) open/shut graticule one ring only 
Type 1: Mark 111 (Projector) dot graticule 
Type 1: Mark 8 (Projector) standard range/base graticule 

The last reflector gunsight produced by Barr & Stroud was based on the
GM2, but incorporated automatic adjustment for elevation and azimuth
(horizontal movement). It was designed for the large anti-shipping
missile of 1945 code-named 'Uncle Tom'. Radar signals were fed into a
computer which energised flexible shafts driving actuators which tilted
or slewed the reflector glass to the left or right, giving a correct
point of aim. Approximately 150 of these intricate instruments were
produced, but the 'Uncle Tom' system was cancelled when the war ended.



The Srb-a-Stys Sight

When Germany occupied the Sudetenland, a Swedish optician working for
the Czech Srb-a-Stys Company was sent to London on a secret mission to
offer a new aircraft gunsight design to the British. The instrument
resembled a large-diameter shortened Aldis sight which needed to be
inserted through the pilot's windscreen. This would have been posed
problems with thick bullet-proof windscreens. Although the sight was
tested and found to be quite accurate, the offer was declined and the
agent, Mr George Vogel, returned to Prague with a letter of thanks to
the Czech Company. 

The caption to the photo is: The Srb-a-Stys optical sight offered to the
Air Ministry in 1938. It was brought to London by a representative of
the Czech company after Germant had marched into the Sudetenland. The
offer was declined with thanks. It would appear that it would have been
even more hazardous than the Mk II in a rough landing. This is the only
known picture of the sight.



Wartime Ring and Bead Sights

Even in the Second World War the ring and bead sight was used
operationally by RAF gunners, because it was not practical to use
reflector sights in some positions. Gunners manning side hatch positions
in flying-boats, observers in naval aircraft, and extra hand-operated
guns in bomber aircraft all used such sights. They were usually the 51
mm (2 in) type, which were far less prone to damage than the pre-war 114
mm (4.5 in). Observers in the Beaufighter T.F.Mk.X had three ring and
bead sights on the single Browning in the cramped rear cockpit. They
used whichever gave a lead on the target. 

Fairey Battle light bombers took a leading part in trying to stop the
German advance into France in May 1940. Their armament, against
high-performance Luftwaffe fighters, was identical to that of the 1917
two-seaters. The observers had a single Vickers K gun, and rarely had a
chance to align their sights onto their opponents, who decimated them.



The Gyro Gunsight Mk I - Pt I

The gyro gunsight at last solved the most difficult problem faced by
pilots and air gunners, that of finding the correct angle of deflection
or 'lead' needed to hit the target when it was moving across the line of
fire. Even experienced fighter pilots had great difficulty in overcoming
the problem. Indeed, the world's top-scoring fighter ace, Eric Hartmann,
revealed that his secret was 'Get in close - down to 25 m - then you
don't need to worry about deflection shooting!' 

When the gyro sight was perfected, no quesswork was needed. The sight
presented an aiming mark which automatically allowed for range,
deflection and gravity drop of the projectiles. As early as 1917 the
basic theory of using a gyroscope as an aid to deflection shooting was
propounded by W/Cdr L.J. Wackett, RFC. With him on the same station was
Capt. (later Prof. Sir) Melville Jones, who was to be a leading member
of the Farnborough gyro team 25 years later. The idea was later
suggested by Dr L.B.C Cunningham of the RAF Education Branch. In 1936 he
pointed out that mathematics could be used to solve any problem of
dynamics; as an example he put forward the theory that even the
complicated problem of air-to-air deflection shooting could be solved
mathematically 'by using a gyroscope to offset the sight line from the
gun line through an angle determined by the rate of turn of the sight
line'. Although his pupils could not understand the implications of his
theory (most of them had no idea what the angle of deflection was
anyway), his observations did not go unnoticed. 

In 1938, with the international situation worsening, the Air Staff
arranged an exercise at Northolt in which all aspects of fighter combat
were to be assessed. The Committee for the Scientific Survey of Air
Defence, headed by Henry Tizard, appointed observers from Farnborough to
advise on points of scientific importance which might be otherwise be
overlooked. 
Camera guns were fitted to many of the aircraft, and a squadron of
Gladiators had just been fitted with some of the first batch of Mk II
reflector sights. When exposed films from the camera guns were examined,
it was found that although the pilots often got into positions to
despatch their victims, very few had any idea of the amount of
deflection needed. 

A report on the findings was duly presented to Tizard, stating: 

Although the new Spitfire and Hurricane fighters performed well, their
effectiveness would be vastly improved if some means could be found to
predict the amount of lead required to hit the target accurately. Many
of the gun camera films proved that if the combats had been in earnest
the enemy would have escaped unscathed. 

The Air Staff were deeply concerned, and the Director of Farnborough was
instructed to investigate the possibility of a predictor gunsight
suitable for use in fighters and the gun turrets of bombers. The problem
was to be given priority over all other work, no expense was to be
spared and the utmost secrecy was to observed. 

Dr Cunningham's theory depended on the fact that a gyroscope will resist
any rotation of its axis. If a gyro is clamped onto a rod on which is
fixed a ring and bead sight, any attempt to follow a crossing target
will depend on the target's crossing speed. A gyro sight would have to
present the marksman with a sight line held back by the gyro, whilst the
line of flight and guns would be in front of this sight line. In other
words, if the pilot kept to the sight line indicated by the gyro, his
guns would automatically point correctly, in direct relation to the rate
of turn. 

By October 1939 two experimental sights of slightly different design had
been fitted to a Hurricane and in the Frazer-Nash FN 25 under turret of
the Wellington. The results of the trials were promising, although the
sights were rather primitive. By the summer of 1940 the RAE Dircetor was
able to report to the Air Staff that a potentially operational sight,
the Mk I GGS (gyro gunsight) was ready for testing. It was given the
code name Type 6 mechanism. 

The Type 6 contained an electric motor driving a rotor mounted on a
stem, the end of which actuated a linkage. Also fitted to the stem was a
saucer-shaped aluminium dome surrounded by four electro magnets. The
motor ran at a speed of 4,000 rpm, so the gyro resisted any angular
movement of the housing. Such a movement tilted the axis of the stem and
the linkage moved a celluloid strip in the optics of a GI primatic
sight. A black ring was engraved on the end of the strip, so that the
gunner saw two graticule rings, one fixed, the other on the celluloid. 

In principle, the Mk I GGS was very similar to a rate-of-turn indicator
which also used a gyro. In this, as the aircraft turned, the gyro held
back the needle of the instrument, this deflection indicating, the force
of the turn with a needle on a dial. In the GGS the gyro resistance was
used to deflect the ring on the celluloid. The electro magnets allowed
for host aircraft speed and height: the thinner the atmosphere, the less
the bullets drop.



The Gyro Gunsight Mk I - Pt 2

As soon as the Air Staff heard that the design had been completed they
made arrangements to rush it into production, the prime contractors
being Ferranti and Elliot Bros. (London) Ltd. But the Director of the
Gunnery Research Unit advised: 

It is the considered opinion of the Gunnery Research Unit that the true
value of the sight cannot be proved without operational trials, and
before full production is authorised we respectfully advise that a
number of Squadrons should be equipped to enable the pilots, after all
the advice that can be given by them, to find for themselves to what
extent it aids them in actual combat. 

Meanwhile, the Air Staff's fears about inaccurate shooting had been
borne-out. Intelligence summaries of combat reports quoted pilots who
could not understand why their fire seemed to have no effect, even when
a long burst was fired from an ideal position. 

In early 1941 Farnborough produced the first pre-production batch of Mk
I gyro sights and a Spitfire and Defiant were flown into the airfield to
be fitted. The sight was rather bulky, and difficult to fit into the
turret of the Defiant. The experienced trials pilots reported an almost
magical performance. As they turned into the attack on the stooge
aircraft, two circles were seen in the eyepiece, the one lagging behind
being the aiming point, the leading circle being the direction in which
the guns were pointing. It was found a little difficult to locate the
target in the small eyepiece, and the circles wandered during a high 'g'
turn, but the correct deflection angle was presented. 

Feranti (Edinburgh) began low-rate production in April 1941, and
Spitfire and Hurricane fighters from operational squadrons tested the
sights in interceptions of German raids during July and August. After
six weeks the AOC Fighter Command, Sir Sholto Douglas, took his eagerly
awaited report (dated September 1941) to Whitehall. It stated: 

The initiative and interest shown in these trials has been far from
satisfactory, owing to the following reasons: the difficulty of carrying
out Service trials of gunsights under operational conditions, and the
reluctance of pilots to use experimental sights in a life-and-death
situation. Also, the restriction that the sight should not be used where
the possibility exists that it might fall into enemy hands has been a
drawback. However, sufficient information has been obtained to enable
the following conclusions to be arrived at: 

1 The hard and angular nature of the sight in the position it occupies
constitutes a danger of facial injury to the pilot in the case of a
forced landing. 

2 The amount of eye freedom is very limited. It is neecessary to place
one eye on the small eyepiece, so it is not posible to observe other
aircraft which would otherwise be seen within the normal field of
vision. 

3 The sight is too sensitive. It requires some device to damp the
violent changes in position of the moving graticule caused by bumps, and
alterations in the rate of turn. Rates of turn above rate 3 cause the
graticule to disappear entirely, and on reappearance it takes one or two
seconds to settle down. It is therefore considered that in its present
form the gyro sight Mk I is not a practical proposition for the
operational requirements of Fighter Command. It is recommended that
consideration should be given to the development of a reflector sight
embodying the principle of the gyro sight, in which the disadvantages
referred to above would be eliminated. The value of training pilots in
the correct amount of deflection to be applied in air fighting has been
considered, and it is proposed to allocate a number of these sights to
Operational Training Units of this Command. 

Bomber Command had also been testing sights fitted in the rear turrets
of Wellingtons. Reports from gunnery officers were more enthusiastic
than those of Fighter Command. Once they had mastered the technique,
turret gunners showed a 50 per cent improvement in marksmanship over
those using Mk III reflector sights. However, as there was no
illumination of the graticule, the sight could not be used at night. The
restricted nature of the small eyepiece was also mentioned, and the
unstable nature of the graticule was a drawback. 

Following these reports, the Air Staff had to postpone full-scale
production. This was doubly disappointing, as the Spitfire Mk V was
being out performed by the new Focke-Wulf Fw 190, and Bomber Command
losses due to German fighters were mounting. Limited production
continued to give trainee pilots and gunners practice in deflection
shooting; some Coastal Command squadrons decided to use the sight
operationally. 

It is perhaps worth outlining again the principles by acting the part of
a trainee turret gunner. You first turn on the switch on the end of the
body. In a few seconds the gyro will run up to 4,000 rpm. To prevent
unnecessary wear, the sight should be switched on only when hostile
aircraft are expected. You then set the aircraft's height and speed on a
control box on the left side of your turret. Looking through the
eyepiece you will see two black circles. The larger graticule is fixed
and indicates the direction in which the guns are pointing. The smaller
ring is the point of aim computed to allow for deflection and bullet
trail. When the turret is stationary and the guns pointing in any
direction other than astern, the moving graticule will be seen as being
displaced from the fixed ring by the four electro magnets. When you turn
your turret to follow a target, the gyro will make the moving graticule
lag behind in relation to the rate of turn or rotation. This lag, added
to the bullet trail allowance, gives the point of aim required to hit
the target - in other words, you can't miss - provided you can
manipulate your turret controls accurately. The range of your sight is
fixed at 274 m (300 yds), which has been found to be the optimum - you
merely place the graticule round the target. The sight is protected from
misting by a filter of silica gel, which dries the air as it enters an
inlet at the bottom of the sight. Two adjusting screws harmonise the
guns with the sight. As the elevation screw is turned part of the
anti-vibration cradle is tilted, causing the line of sight to be
elevated or depressed. Similarly, as the traverse screw is turned, the
line of sight is rotated in azimuth. 

The Farnborough team worked urgently to overcome the problems noted in
the Fighter Command report. The first and most serious fault was the
means of display. It had been decided to base the display of the Mk I on
the optics of the GI to save time, but the choice of this system had
precluded night use, and the small eyepiece was far too restrictive. The
obvious answer was to insert a moving graticule into a reflector sight,
as suggested by Sholto Douglas.



The Gyro Gunsight Mk II - Pt I

Farnborough devised a solution which was one of the simplest yet most
effective inventions of the war: a mirror was fixed to the end of the
gyro and made to reflect an illuminated graticule onto the reflector
plate. This graticule moved to the correct position allowing for
deflection, and also incorporated a ranging facility. The graticule
consisted of a ring of six small diamonds, the diameter of which could
be set to correspond with the target span. The type of enemy aircraft
was set on a dial, enabling the sight to calculate the range. The
reflector screen was a large glass plate 120 mm (4.7 in) x 64 mm (2.5
in). Looking into the screen, the operator saw two illuminated
graticules. The one on the left was a fixed ring graticule which could
be used if the gyro system failed, its main use being to harmonise the
guns with the sights. In the right half of the screen was the
gyro-controlled ring of six diamonds. The diameter of the ring was
adjusted by foot pedals in the turret version of the sight, and by a
twist grip on the pilot's throttle lever on the fighter type. Both
graticules could be dimmed for night use, or used singly by switching
either on or off. The height and speed setting unit of the Mk I was
found to be ideal, and could not be improved. The first Mk II sights
made at Farnborough were tested by the Armament Research Unit in July
1943, and it was clear that the problems had been solved.



The Gyro Gunsight Mk II - Pt 2

The new sight had had the undivided attention of some of the most able
brains in the country, some of those taking part under Sir Melville
Jones being A.A Hale, B. Sykes and G/Capt. Ford. Ferranti played a
central role in the design and development of the complex gyro and
electrical components. The sight was to be known as the GGS Mk IIC
(turret) and Mk IID (pilot). Deliveries from a purpose-built factory
near Edinburgh began in late 1943. 

The sights seemed to possess almost magical qualities. As an ex-Battle
of Britain pilot stated: ' I look back on previous combats where the
enemy escaped more or less intact, and realised that I could most
certainly and easily have destroyed it if I had been using a good
gunsight'. A demonstration was also staged for two pilots of the USAAF.
One reported: 

I believe this sight would improve gunnery at least 100 per cent.
Shooting is at the moment for most pilots purely guesswork. A pilot
cannot guess with this sight, due to this I am sure that at least the
lower bracket of pilots (75 per cent) will improve their shooting to the
level of the best gunnery shots now, and the best ones can do even
better. It is easy to handle, and there is no situaiton it cannot handle
as well as the GM2, and in most cases (90 per cent) it will do better. 

The second pilot reported 

Speaking from the point of view of the day fighter, I would say that the
Mk IID gyro gunsight is definitely the answer to our problem with
deflection shooting. We are proving daily that the average pilot cannot
do deflection shooting, even with small angles, accurately with a fixed
sight. I think that the sight should be put into produciton immediately
and fighter squadrons equipped with them as soon as possible. 

Bomber Command were also very keen to receive the Mk IIC version. It was
first issued to gunnery schools and operational training units where
lectures and air-to-air gunnery practice were quickly arranged. The
gunnery schools had been very pleased with the Mk I sight, which had
proved invaluable for instructional purposes. A compact 16 mm
sight-recording camera had been produced, and gunnery training was much
improved owing to the fact that no ammunition needed to be fired, and a
record of accuracy could be shown to the trainee. As with the Aldis
sight, word soon spread round the operational squadrons and the new
sight was eagerly awaited.



The Gyro Gunsight Mk II - Pt 3

At first there was concern over the possibility of the sight falling
into enemy hands, and there were restrictions on gyro-equipped aircraft
flying over enemy-held territory, but as they became more numerous this
rule was relaxed, and the Luftwaffe began to suffer from the attentions
of an enemy who could suddenly fire with uncanny accuracy. Not that all
fighter pilots accepted the gyro sight with enthusiam at first, for it
required a fair degree of dexterity: select graticule brillance, set
graticule presentation, set span level, then once the target is
presented align the ring of diamonds to the enemy span. No such
preparation was needed on the Mk II, but as pilots gained experience the
early scepticism vanished, and results bore witness to the gyro's
effectiveness. The US Navy and Army Air Force formally accepted the
sight, and production commenced in America where it was designated the
Mk 18 (Navy) and K-14 (USAAF). In Canada, Semco Instruments produced a
naval sight more robust than aircraft versions and with two dimming
screens to counter glare off the sea. Otherwise the 'works' were
identical to the Ferranti model. 

perhaps the reader can imagine himself seated in the Frazer-Nash FN.20
tail turret of a Lancaster, flying in daylight over Germany in early
1945, when an enemy fighter is seen to dive to the attack. 

The heart misses a beat, but then you realise that only you can save the
aircraft and crew, you are in effect in full control. First you inform
the captain and crew of imminent attack, and tell the pilot which way to
break away to give the enemy maximum deflection. You will have already
set the height and speed on the dials of the control box mounted
horizontally at hand level to your right. You identify the fighter and
set its wingspan on the span handle. You now operate the left pedal
which opens the ring of diamonds to the maximum range setting. As your
attacker closes in, you keep him inside the ring until he fills the
ring; he is now framed and within range - open fire with a four-second
burst. As long as you can keep him centre in the ring your bullets will
be striking home. If he keeps coming in, he will appear to get larger;
depress the right pedal to control the ring and keep his wingtips
touching the diamonds. Track the target accurately and smoothly at the
same time as closing the range with the pedals. When the target reaches
183 m (200 yds) the graticule will not get smaller, but the sight will
still be accurate. Keep the right foot pressed and aim at the aprt of
the fighter where hits will do the most damage.



The Gyro Gunsight Mk II - Pt 4

A fighter pilot using the Mk IID would not use pedals to control the
diamonds but a twist grip on his throttle. The operator could select
various combinations of illumination. With Gyro Night, only the gyro
graticule was visible, and the range was set to 165 m (180 yds)
irrespective of pedals or twist grip. This was the usual maximum range
at night. 

Several types of German aircraft were marked on the dial, and aircraft
identification became even more important to pilots and gunners. Gunners
were taught to recognise the frontal silhouettes of German and Allied
aircraft instantly. Anyone who failed the aircraft recognition test
badly often failed the course. 

Caption to middle sketch: The American version of the GGS, the K-14
showing its operating sequence. 

Caption to bottom sketch: The graticule selector/dimmer unit. The fixed
graticule was used mainly for gun harmonising, but was also a standby in
case of gyro failure. 

Details of Mk II GGS Gyro Sight Production 

GGS specification received from Air Ministry to Ferranti Ltd, Edinburgh,
February 1943. 
Site for new factory purchased December 1942. 
Building commenced February 1943. 
Factory opened June 1943 
First production sight 30 November 1943 
Quantity production commenced February 1944 
Output by March 1945: 1,000 

From a labour force of 100 in July 1943, Ferranti employed 950 at peak
production in October 1944. 

Number produced. 

1944 

February: 8 
March: 110 
April: 200 
May: 250 
June: 370 
July: 380 
August: 420 
September: 540 
October: 700 
November: 720 
December: 600 

1945 

February: 400 
March: 1,000 
April: 1,100 

Other companies were also involved in production: Barr & Stroud supplied
lenses and produced a small quantity of complete sights. Salford
Electrical Company produced gyro sights to Ferranti drawings, and other
concerns carried out sub-contract work.



Ventral Turret Sights

Afrer suffering a high loss rate in the early months of the war, the
Blenheim light bomber was fitted with a rearward-firing under turret,
the FN.54A. The twin Browning guns were aimed by a periscopic sight, the
Type A. This consisted of an optical tube with a mirror at each end, a
graticule and angle-of-drift scale. The two operating handles each had a
trigger, and the graticule was a black circle. The field covered was 20
degrees each side, and 17 degrees depression. A more elaborate sight was
fitted to the Frazer-Nash FN.64 fitted to some Lancasters. This, the
Type B, featured a full optical system culminating in a prism linked to
the guns in elevation. The turret was powered by a small version of the
Nash & Thompson hydraulic system. As in all prismatic systems, the
gunner's vision was limited to the narrow FOV through the lenses.



The Thompson Sight

In 1941-42 the Royal New Zealand Air Force base at Wigram had a fitter
armourer, Cpl. John R. Thompson, who had already invented various
gunnery devices, devised a sight which gave the gunner a point of aim
which predicted the angle of deflection. In theory, the firer matched
the target's path and speed with a moving graticule pattern seen through
a screen similar to that of the Mk II reflector sight. The gunner
controlled the moving series of graticule sections engraved on an
endless belt of heat-resisting 16 mm film, the direction of the
graticule being aligned with the apparent path of the target. After a
period of tracking, when the target was made to move towards the centre
of the sight, the guns were fired when the target reached a line marked
across the graticule movement. He produced the drawings and prototype in
nine weeks (the Mk IIC gyro sight was developed in 12 months). 

Any technical invention of this kind is often met with scepticism by the
authorities, and Thompson's was no exception. It was only after a
desperate letter to the Chief of the Air Staff dated 26 May 1943 that he
was summoned to Britain with his invention, which was evaluated at
Farnborough. Unknown to Thompson, the gyro sight was nearing completion,
but his sight was thoroughly tested by the Armaments Section. The
relevant parts of their conclusions were as follows: 

The sight presents to the gunner a collimated graticule which consists
of a broken line which can move across the field of view in the
direction of its length at a rate which can be controlled by the gunner.
The orientation of the travelling line can also be controlled by the
gunner, in such a way that it always travels through a central point in
the field of view to which the guns are organised. No arrangements for
including trail and gravity drop allowance are included. 

The sight therefore demands: the setting of guns and graticule pattern
to cause the target to fly towards the centre, matching of the apparent
graticule speed and the apparent target speed, tracking the target with
the aiming point thus determined and judgement of the firing range with
stadiametric aid of breaks in the graticule pattern. 

The defect of the principle is that the angular velocity of the target
is determined sometime before firing, and is determined relative to the
gunner's aircraft which must, therefore, fly straight and level if large
errors are to be avoided. The operations required of the gunner could
present him with difficulty under combat conditions, and the addition of
trail and gravity drop allowance would further complicate what is
already an involved mechanism. 

This sight is a good attempt at the solution of the problems of
controlling aircraft guns, and the engineering skill displayed in the
design of the prototype is high. The arrangement is, however, outdated
by other developments in Great Britiain and in the USA: in particular
the British GGS Mk IIC sight is more compact, is likely to be simpler to
use, is referred to space axes rather than own aircraft axes, and
includes trail and bullet drop. In view of the fact that this
development is in production, further work on the Thompson sight is not
recommended. 

It is recommended, however, that this inventor be encouraged to consider
further problems, since the skill and thought shown by his prototype
sight is of a high class. 

Thompson returned to New Zealand where he continued to work as an
engineering officer in the RNZAF. Until 1942 no such sight had been
developed by any nation. Thompson's achievement must rank amongst the
most remarkable of the war. The official assessment was probably
correct, but if the gyroscopic sight had not materialised there is every
possibility that the Thompson sight would have been adopted by the RAF.
Before the sight was sent to Britain it was demonstrated to a group of
visisting operational pilots of the RNZAF, including W/Cdr Wells, who
described it as 'the answer to a fighter pilot's prayer'.



Airborne Interception Radar Gunsighting

Well before the war it had been realised that if daylight bombing
attacks were successfully countered, a future enemy would switch to
raids under the cover of darkness. When 'radiolocation' was seen as
feasible, a design team was set up at Bawdsley in Suffolk to investigate
the possibility of airborne radar detection for night fighters. This
project, under the direction of Dr E. G. Bowen, produced the first
successful airborne radar sets. The first equipment was limited by
having a frequency of 1.5 m (1.64 yds), which gave a very wide beam and
limited range. However, these first sets were successful in detecting
intruders. After the invention of the cavity magnetron by Messrs Randel
and Boot, and the Klystron oscillator, it was possible to produce a
radar of 10 cm (3.9 in) frequency, giving a narrow beam of 30 degrees,
which was less prone to ground returns. 

In March 1941 the first airborne centimetric radar was tested in a
Blenheim by Alan Hodgkin of the TRE and Edwards of GEC, the prototype
system being known as the AIS. In autumn of 1941 sets had been delivered
for service trials by Beaufighters for the FIU (Fighter Interception
Unit) and 100 sets were ordered from GEC with Nash & Thompson scanners.
The first produciton model was the Mk VII, the first squadron being
equipped in March 1942. The first kill was recorded in April 1942,
followed by 100 more in the following months of the year. 

The Mark VIII 

These radars were designed for two-man operation: the radar operator
viewed the screen and gave the pilot instructions for the interception.
A modification to the earlier Mk V was the 'windscreen project', which
consisted of a unit which projected the image of the radar display up
onto the pilot's windscreen. It was seen as a step forward and the
system was tested at Farnborough, but it was not adopted for service.
However, an improved version was designed for the main production
version, the Mk VIII. This proved successful but was not adopted for use
at that time. The official description of the projector system read: 

The windscreen projection endeavours to combine the four main functional
aids into a single co-ordinated picture showing the pilot what is
happening, and enable him to carry out the interception by its sole aid.


The whole picture is therefore projected ahead of the aircraft, and
observed by the pilot looking through his windscreen. The pilot sees the
position of the enemy aircraft and its range, his own position relative
to it, and his altitude in relation to the horizon and a pre-set
heading, the whole being encompassed by the gunsight circle. In this
way, many difficulties experienced while carrying out a night
interception are hoped to be successfully overcome. 

Firstly, the pilot's attention will not be divided between several
instruments in his cockpit, concentration will thereby be enhanced at
the expense of less strain and time lags reduced. Secondly, the pilot
will be in the most favourable condition to achieve a visual since his
dark adaptation will be the best possible for the existing night
conditions, his eyes will be focused to infinity. Additionally the
visual will be aided by the fact that the pilot will be looking out in
the direction of the enemy aircraft. Lastly no change in the pilot's eye
position will be required throughout the whole interception, since the
gunsight ring is included in the picture. 

A particular development of the system has been carried out for use with
AI Mk VIII to provide the pilot with blind flying information. 

Method of Operation of the AI Mk VIII Projector System 

When the set was switched on the pilot adjusted the tube brightness and
background control; the radar scanning system then began to operate.
When a target was detected an electronic spot or 'blip' appeared on the
screen, showing the position in relation to the pilot's field of view.
The aircraft was then brought into a position where the blip was
central. When the range had decreased to 2,286 m (2,500 yds), small
horizontal lines or 'wings' began to grow on either side of the blip.
The pilot then had to reduce speed to avoid overshooting the target.
From this time, depending on conditions, the target was likely to be
seen. The gunsight would have been switched on during the search period
and adjusted for brightness. When the target was seen the radar image
was turned off, leaving only the gunsight graticule visible. The pilot
then opened fire. 

Other facilities available from the system was IFF (Identification
Friend or Foe) and a heading indicator consisting of a vee in the
horizon position line which could be set to a beacon or specific
heading. Identifiable ground returns noticed during the operation of
airborne radar sets led to the development of blind navigation by Dr
Bernard Lovell which later became the H2S navigation and blind bombing
system. 

As can be seen by the above description, this system could be regarded
as the ancestor to the modern HUD (head-up display). The information
projected onto the windscreen consisted of an artificial horizon, target
poistion and range, and a gunsight graticule. The gunsight consisted of
a lamp in a quick-release housing illuminating a 160 km/h (100 mph) ring
and dot graticule. Interposed between the lamp and graticule unit was a
hemispherical shutter, pivoted and rotated by a lever, which, when
rotated, shrouded the ring, giving a spot graticule only (as in the
Beamont modification). The graticule image was projected through a prism
and a stadiametric lens system onto the windscreen, and a dimming
rheostat was fitted close to the unit on the instrument panel. Pilots
who used the Mk V and Mk VIII equipment suggested that as the
directional gyro heading indicator (pre-set heading) was rarely used, a
more useful aid would have been a presentation of airspeed - an
essential ingredient of night interception.



Bomber Command Tracer Ranging

Though tracer was known to be a misleading aid, on 8 April 1940 the
Farnborough Gunnery Research Department issued a report to Bomber
Command gunnery leaders entitled "The use of tracer ammunition as an aid
to air sighting". The reason for this was an unforeseen problem
encountered by rear gunners. It was found that, when a fighter
approached on a 'curve of pursuit' (a turning attack, keeping his guns
aligned on the bomber), it was very difficult to make a correct
allowance for deflection. This was because a tail gunner had nothing to
tell him whether an attacking fighter was moving across his line of fire
or not. The gunner had the impression of being suspended in space. 

After many novel ideas had been tried, it was found that the solution
was the use of tracer. The tracer then in use was the Type G Mk IV,
which burned to 549 m (600 yds). The theory was that this would help
solve problems with both range and deflection. The advice given was: 

As the fighter approaches at long range fire a burst, keeping the centre
dot aligned on the target. You will see the tracer rise to the centre of
the ring, remain in a cluster, then move sideways in the direction from
where the fighter has come. This gives a clear indication of the
allowance required. Adjust your line of fire in the opposite direction
of the movement. 

Commence firing when the target is just over half-way along the trace,
then maintain your aim and keep firing until the range closes to 138 m
(150 yds) then fire point blank. 

The amount of deflection was set out in a directive entitled 'Zone
system of sighting allowance'. It gave a series of allowances, such as :
'when a fighter is seen in the sector between 10 degrees and 30 degrees
round dead astern, allow two rads (radii of the graticule circle). This
may seem complicated, but failure to grasp such advice could mean the
loss of an aircraft and crew. Any fighter pilot engaging an aircraft
with a skilful rear gunner did so at his peril. A Sunderland on convoy
patrol off Norway was attacked by a group of Ju 88s which dived on the
flying-boat in pairs. After an hour two of the Junkers had been shot
down, and the Sunderland returned to its base at Invergordon. 

Various types of tracer were designed by ICI Kynoch. One type burned red
to 366 m (400 yds), then a brilliant red, before ending in a puff of
smoke. This was to warn the pilot that is ammunition was nearly spent.
The G Mk III did not trace until 183 m (200 yds), to avoid giving away
the position of the aircraft. The Luftwaffe did not use ball ammunition
in its 7.92 mm guns: ammunition comprised tracer, AP and incendiary
rounds. 

Over-The-Nose Sighting 

The Spitfire, like many fiighters, gave the pilot a poor view ahead over
the long nose cowling. When an enemy was engaged from behind, the point
of aim had to be slightly above the target to allow for bullet drop, and
when the target was climbing away the pilot needed a lead angle above
his quarry. In these situations the pilot had to ease the nose down and
observe the target, then pull the nose up slightly and press the gun
button. 

In early 1942 a periscopic device was tested at the Air Fighting
Development Unit at Duxford with a view to overcoming this problem. A
Spitfire Mk II (converted Mk I K9830) was fitted with two mirrors, one
mounted just behind the gunsight, and the other, much larger, fixed
inside the top of the windscreen looking forward into the bliond area.
It gave the pilot vision into the blind zone, but it was difficult to
keep the target in view once the nose was raised, and was not a
practical proposition for the extra few degrees of vision gained. The
officer in charge of the tests duly reported these findings and the
device was not accepted for Service use.





-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Brian Ellis
Sent: den 1 september 2007 09:31
To: [log in to unmask]
Subject: [TN] OT: reminiscences

When I was a student, in 1948, I took a summer job with a company making
aircraft gyroscopic gunsights. My work involved:
1. mixing potassium bichromate with fish glue 2. applying a coat of this
mix to a very thin blackened steel sheet 3. after drying, exposing same
to UV light through glass photographic plates with registration pins,
turning over and doing the same on t'other side (different plate) 4.
developing the image with hot water 5. etching the sheet in nitric acid
6. rinsing in clean water 7. stripping the resist in boiling strong
sodium hydroxide solution

The result was about twenty graticules with two curved, very fine,
slots. If two were placed back-to-back, depending on their respective
positions, two dots of light shone through. These were projected on a
half-silvered mirror and the gunner would turn a knob to align the two
dots of light with the wingtips of the enemy aircraft, to get the range.

This was a very hazardous job but it was my first (but not last!)
experience of using a photoresist for etching a metal. Can anyone beat
this kind of work, going back 59 years? :-)

Brian

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