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THE AIRCRAFT GUN
The RAF then became interested in fitting the Molins Gun in the de Havilland Mosquito, to form an airborne anti-tank weapon to replace the Hurricane IID which had been equipped with a pair of Vickers 40mm Class S guns.
The aircraft was duly developed as the Mosquito FB Mk XVIII, popularly known as the "Tsetse", but by this time the RAF had lost interest in the anti-tank gun role so the aircraft were brought into service by Coastal Command for anti-ship (and specifically anti-U-boat) purposes. The Tsetse, of which about thirty were built, served with No.248 Squadron during 1944 and is credited with sinking a U-boat.
Perhaps its most remarkable achievement occurred during an anti-shipping strike, when one Tsetse became involved in a melee with defending Luftwaffe aircraft. A Junkers 88 was careless enough to fly in front of a Tsetse, which promptly fired its big gun and demolished the Ju 88 with one shot!
The Molins Gun, which was technically known to the RAF as the "QF 6pdr Class M Mark I with Auto Loader Mk III" was based on the long-barrelled (50 calibre) gun. The gun weighed 487 kg (635 kg with autoloader) and was fully automatic, with a rate of fire of about 55 rounds per minute. The ammunition supply in the autoloader consisted of 21 rounds, held in five racks of unequal length, plus two additional rounds in the feedway. The rounds in each rack were fed by a combination of gravity and a spring-loaded arm and each rack was moved into place in turn by an electric motor. The gun normally used the plain AP shot (that is the only one shown in photographs), so had a high muzzle velocity of 890 m/sec (2,920 fps). Against U-boat hulls, it was calculated that it would be able to penetrate the hull when striking at an angle of 45 degrees or more, at a range of about 1400m, even through 60cm of water. The gun/aircraft combination was extremely accurate, achieving a hit rate in training of 33% against tank-sized targets - compared with 5% for rocket projectiles. The Tsetse was eventually withdrawn from service when the RAF decided to use rocket projectiles for such roles because, despite their relative lack of accuracy, these were more suited to a variety of purposes and could easily be fitted, or removed, as required.
The Molins Gun in the Mosquito FB Mk XVIII was tested in the USA in 1945, in comparison with the nearest US equivalent, the manually loaded 75mm AN-Mk 5 in the PBJ-1H. This comparison was more valid than the difference in calibre might suggest, for the 75x350R ammunition used in the American gun (the same as was used by the M4 tank gun in the Sherman) was about the same overall size as the 57x441R, and the 6pdr and 75mm tank guns were effectively interchangeable in the later British tanks.
The Molins Gun impressed the Americans with its performance and reliability and was considered superior to the 75mm as it could achieve a much higher rate of fire. It was noted that fairly violent evasive action and 2.5 positive Gs did not cause stoppages - which could not be said for manual loading!
The Americans recommended that the Molins autoloader could be considered as suitable not just for conventional guns but also for recoilless weapons and spin-stabilised rockets.
