Anti-Aircraft Guns aim at the Bombers

The coastal Observer Corps spoted enemy aircraft and set the defence machinery in motion. The listeners manoeuvred their huge "ear trumpets" to the exact spot where the noise was greatest. This gave the direction and height of the aircraft, enabling the three searchlights to be accurately pointed. On the command "expose," the enemy bombers would have been illuminated. The interceptor fighters attacked, while the height-finder crew measured the height of the bombers and passed this on to the predictor. The predictor calculated the bearing, elevation, and fuse setting for the shells to burst at the correct height, and also allowed for wind curve of the trajectory and barometric pressure in the upper air. All this information was automatically passed to the dials of the A.A. gun.

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The Gun's Crew

3.7-inch A.A. guns were each worked by a crew of nine. Two of the crew would bring up 28.lb. shells and after the fuses had been set by an automatic fire setter, the shells were placed as required in the loading tray. This was then swung over into line with the open breech. A third man rammed it home with the wire operated ramming device. The breech did not close completely until the loading tray was returned to its original position.

How the Gun Works

The shock of discharge was absorbed by a recoil system embodying a recoil cylinder which, by means of compressed air, not only brought the gun to rest at the end of the recoil and returned it to the firing position, but opened the breech and ejected the empty cartridge case. So the breech lever was used only when starting the gun, and thereafter the gun operated automatically. The action of ramming home the cartridge, closed the breech and operated the firing-pin in the breech block.

Bringing the Gun into Action

The 3.7 gun was mounted on four balloon tyres and was towed by a Scammell tractor up to 30 mph on a good road and could also have been taken across country. The gun was brought into action by lowering it with its platform on to the ground and removing two of the wheels; the remaining two serving to stabilise the gun in action. Four thrust girders with levelling plates radiated from the platform and were screwed to the ground. The gun mounting would have been precisely levelled before exact firing could be obtained.