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 above text and photos were taken from "British Aircraft Armament Vol.2; Guns and Gunsights", by R Wallace Clarke
You do not have the required permissions to view the files attached to this post.