In 1936
Royal Aircraft Establishment scientist
Leslie Bennet Craigie Cunningham suggested using a
gyroscope's resistance to rotation to modify the aiming point in a gun sight to compensate for
deflection caused by a turning aircraft. This arrangement meant the information presented to the pilot was
of his own aircraft, that is the deflection/lead calculated was based on his own bank-level, rate of turn, airspeed etc. The assumption was that the flight path was following the flight path of the target aircraft, as in a dogfight, therefore the input data was accurate enough to provide useful output data to the pilot.
British developments Mark I After tests with two experimental gyro gunsights which had begun in 1939, the first production gyro gunsight was the
British Mark I Gyro Sight, developed at
Farnborough in 1941. To save time in development the sight was based on the already existing type G
prismatic sight, basically a telescopic gun sight folded into a shorter length by a series of
prisms. Prototypes were tested in a
Supermarine Spitfire and the turret of a
Boulton Paul Defiant in the early part of that year. With the successful conclusion of these tests the sight was put into production by
Ferranti, the first limited-production versions being available by the spring of 1941, with the sights being first used operationally against
Luftwaffe raids on Britain in July the same year. The Mark I sight had a number of drawbacks, however, including a limited field of view, erratic behaviour of the reticle, and requiring the pilot/gunner to put their eye up against an
eyepiece during violent manoeuvres.
Mark II Production of the Mark I was postponed and work started on an improved sight. Changes involved incorporating the gyro adjusted reticle into a more standard
reflector sight system, a non-magnifying optical sight that had been in use since 1918. Reflector sights consisting of a 45-degree angle glass
beam splitter that sat in front of the pilot and projected an illuminated image of an aiming
reticle that appeared to sit out in front of the pilot's field of view at infinity and was perfectly aligned with the plane's guns ("
boresighted" with the guns). The sight sat some distance away from the pilot, so it was safer to use and didn't impair the pilot's field of view. The optical nature of the reflector sight meant it was possible to feed other information into field of view. In the reflector sight version, range was measured by comparing the wingspan of the target seen through the sight to a pre-set number. The pre-set number was selected via a large dial on the front of the sight, and the range was then measured by turning another dial on the aircraft's throttle. This new sight became the Mark II Gyro Sight and was first tested in late 1943 with production examples becoming available later in the same year. Ferranti built a new factory in the Crewe Toll area of
Edinburgh, Scotland to build the sights. This factory would later go on to be the centre for Ferranti's long history in
radar development. The
Mark II was also subsequently produced in the
US by
Sperry as the
K-14 (
USAAF) and
Mk18 (
Navy). The K-14 included two projector systems for the reflector sight, one with gyro correction for attacking aircraft, and a second for attacking ground targets. It was otherwise similar to the British models, although the dial for adjusting the target size was moved to the left side of the sight instead of the front. The area where the Mark II had the dial was replaced by a moving scale that indicated the current range to the target, along with a large pad that prevented pilot head injuries in the case of rapid deceleration. The
radar-aimed
AGLT Village Inn tail turret incorporated a Mark II Gyro Sight and this turret was fitted to some
Lancaster bombers towards the end of
World War II.
German developments Although since 1935 the relevant German companies offered the
Reich Air Ministry (RLM) a new type of gyro-stabilized sight, the well-proven REVI (
Reflexvisier, or reflector sight) remained in service for combat aircraft. The gyro-stabilized sights received the designation of EZ (
Eigen- und Zielgeschwindigkeitsgesteuertes Visier, or enemy and
indicated airspeed-controlled sight), such as EZ/REVI-6a. The development of the EZ 40 gyro sight began in 1935 at the
Carl Zeiss and Askania companies, but was of low priority. In the summer of 1941, the EZ 40, for which both the Carl Zeiss and Askania companies were submitting their developments, was rejected. Tested in a
Bf 109 F, Askania's EZ 40 produced 50 to 100% higher hit probability compared to the then standard sight, the REVI C12c. It was however too large and unstable. In the summer of 1943 an example of the EZ 41 developed by the Zeiss company was tested, but was refused because of too many faults. In the summer 1942, the Askania company began work on the
EZ 42, a gunsight which could be adjusted for the target's
wingspan (in order to estimate distance to the target). The EZ 42 was made up by two major parts, and lead computation was provided by two gyroscopes. The system, weighing 13.6 kg (30 lb) complete, of which the reflector sight was 3.2 kg, much larger than allied models. Three examples of the first series of 33 pieces were delivered in July 1944. At this time, the Germans became aware that the British were using gyroscopic sights in their fighters, so the decision was made to rush sights into mass production at the Steinheil company in
Munich before trials were fully complete. Thus, these were followed by further 770 units, the majority being built in early 1945. Each unit took 130 labour hours to produce. Approximately 200 of the sights were installed into
Fw 190 and
Me 262 fighters for field testing. The pilots reported that attacks from 20 degrees deflection were possible, and that although the maximum range of the EZ 42 was stated as approximately 1,000 meters, several enemy aircraft were shot down from a combat distance of 1,500 meters. The EZ 42 was compared with the Allied G.G.S. from a captured
P-47 Thunderbolt in September 1944 in Germany. Both sights were tested in the same Fw 190, and by the same pilot. The conclusion was critical of the moving graticule of the G.G.S., which could be obscured by the target. Compared to the EZ 42, the Allied sight's prediction angle was found on average to be 20% less accurate, and vary by 1% per degree. Tracking accuracy with the G.G.S. measured as the mean error of the best 50% of pictures was 20% worse than with the EZ 42. Under postwar interrogation, German technical staff said that they felt that the trial methodology was inadequate, while
RAE assessed the results to be of doubtful validity, noting in addition that the German system would be subject to considerable altitude and temperature sensitivity. The British were also very critical of the "extremely simple" training offered on usage of the sights. Major
Rudolf Sinner of
JG 7 opposed their installation in his fighters after a demonstration in February/March 1945, finding the need to constantly adjust range to be unsuited to jet combat tactics. ==Usage (Mark II Gyro Sight)==