You’ll be wanting a copy of Ian V. Hogg’s “British and American Artillery of World War Two”.
The 3.7” QF in mounting Mk 3A was the Mk 3 with MFS No. 11. The Mk 3 being the mobile mounting for wartime production with the most visible change being the gunlayers facing to the rear. The MFS No. 11 was the Molins Fuze Setter in which a round was dropped into a tray and the infamous “Pig’s Ear” switch flap slapped and subsequently the time fuze was automatically set while automatically loaded. The Mk 3A was only second to the static Mk 2B in service and use during WW2. The other main version of the 3.7” was the high velocity Mk 6 ordnance in Mk 4 mounting which had the longer 65 calibre barrel, with variable depth rifling and a bigger cartridge case. This was the 3.7” mainstay after the war.
Rate of fire of the Mk 3A was 25 rpm thanks to the MFS and up from 10 rpm with manual fuze setting and hand loading. Later weapons like the Green Mace were able to achieve much higher rates of fire because they didn’t need fuze setting thanks to radar proximity fuzes (and IR proximity fuzes in current large calibre anti aircraft guns).
Interestingly at the end of the war the Germans were considering doing away with the set time proximity fuze altogether. Dr Voss, a research scientist at the RLM, had shown that the Pk between heavy FlAK firing full calibre, time fuzed ammunition (using clock work fuzes) was actually lower than if they were firing contact fuzed sub calibre ammunition. Because of the lower rate of fire caused by fuze setting, predicator range error, the longer time of flight and the failure rate of clock work fuzes. Also compounded by the actual lethal distance of even an 88mm air burst shell (only 9m/30’) compared to a direct hit. Combat trials showed the new method firing sub calibre (55mm with 0.5kg HE content) contact shells was much more effective but conservatism in the Luftwaffe meant the full switch was not ordered until late March 1945 when of course it was too late. In addition the new FlAK approach required significantly less steel for ammunition which was strategically important but the psychological effect of a “silent” FlAK barrage remains to be seen… Though it may be worse on a formation or stream once kills are made.(Data from Ian V. Hogg’s “German Artillery of World War Two”)
