Sorry to be an interloper on this thread but this is something of my subject.
The ‘villain of the piece’ was the Air Ministry (AM) - ably aided and abetted by, yes, the Treasury - who specified the (rimless cartridge design) .30 Browning M/G in the mid 30’s, as the successor to the WWI vintage .303” Lewis and Vickers M/Gs; except that, as there were millions of (rimmed) .303” rounds in store from WWI production, the AM dictated (at the insistence of the Treasury) that the proven and reliable .30 Browning had to be modified to fire the different calibre and cartridge design. Of course, in time honoured tradition, this proved more difficult (and expensive and time-consuming) than anticipated and led to an almost total redesign of the weapon (No, REALLY?!), which is one reason why the (single) drum-fed Vickers ‘K’ (or GO) was adopted for bomber defence on Blenheims, Battles, Swordfish, Hampdens and other multi-seat aircraft of that timeframe, but that’s another story.
By the time the .303” Browning entered RAF service it was recognised that the .303” round was of insufficient hitting power and that the standard 2 or 4-gun installations specified for bombers (tail) and fighters respectively were upgraded to 4 and 8-gun installations to increase the weight of fire delivered in a specific timeframe. However, the die had been cast and the .303” calibre was what we went to war with.
In the meantime, the AM then attempted to redress the situation by changing policy towards adopting a larger calibre weapon, but - given the rate of development in aircraft performance and armour protection – decided to ‘skip’ the .5” Browning option (baaaad move) and go straight to the 20mm cannon, adopting the Hispano; the gun itself was a good design, it was the feed mechanism that was a long time in gestation.
The AM was loath to tamper with the production lines of our heavy bombers and Sir Arthur Harris waged a ding-dong battle with them to try to get the .5” M2 Browning introduced into service with Bomber Command as the USAAF had proven this to be an entirely adequate and reliable weapon for bomber defence.
So exasperated did Harris become that he bypassed the AM entirely and went straight to Rose Bros of Gainsborough and asked them to design a twin .5” Browning turret that could be a direct ‘drop-in’ replacement for the normal FN (1)20 4 x .303” turret on Lancasters and assigned Air Cdre Rice to work directly with Rose Bros to make it happen – hence the Rose-Rice turret (mentioned previously) that was beginning to be retrofitted to Lancasters of No 1 Gp in Lincolnshire from late 1944 onwards. However, as also mentioned above size and weight of the heavier calibres is very important and, whereas the FN 120 turret had 1,000 rounds of .303” available for each rear turret gun of a Lancaster, the Rose-Rice turret only had 335 rounds per gun; but, of course, it’s where they hit that’s important!
The reason Harris went to Rose Bros was that they had quickly and effectively designed for him (when he was AOC 5 Gp at the beginning of the war) a mounting for the upper and lower Hampden rear gun installations that doubled the firepower of each position from 1 x Vickers K to 2. His actions in bypassing the bureaucratic AM processes demonstrates his concern for his crews’ welfare and operational longevity and gives lie to the oft-repeated falsehood that Harris was dismissive of his crews’ wellbeing and treated them, literally, as cannon-fodder. His nickname to his crews was ‘Butch’, which is NOT a contraction of ‘Butcher’, as the post war revisionists would have you believe – it was a common nickname of the time.
The ‘official’ AM sponsored 2 x .5” browning turret (the FN 82) entered service in June 1945……….need one say more?
Finally, the usually accepted definition of an autocannon is a weapon that fires explosive rounds. The smallest calibre is generally accepted as 15mm as evidenced by the 15mm MG 151/15 cannon fitted in the engine mounted Bf109 F-2 firing through the propeller hub; later replaced by the 20mm MG151/20 in the ‘109 F-4.
Sorry about the long post!
FLYER Club Member
