Ministry of Aircraft Production.
| Date | %US | US 1 stage | M28 | M29 | M31 | US 2 stage |
Aug-41 | 50.0 | 2 | 2 | | | |
Sep-41 | 25.0 | 1 | 3 | | | |
Oct-41 | 40.0 | 2 | 3 | | | |
Nov-41 | 30.0 | 3 | 7 | | | |
Dec-41 | 34.6 | 9 | 17 | | | |
Jan-42 | 32.1 | 35 | 74 | | | |
Feb-42 | 32.2 | 48 | 22 | 79 | | |
Mar-42 | 34.5 | 115 | 57 | 160 | 1 | |
Apr-42 | 33.3 | 168 | 334 | 1 | 2 | |
May-42 | 32.2 | 194 | 406 | 0 | 2 | |
Jun-42 | 34.5 | 242 | 458 | 0 | 2 | |
Jul-42 | 28.0 | 224 | 528 | 36 | 13 | |
Aug-42 | 23.8 | 190 | 505 | 82 | 23 | |
Sep-42 | 23.8 | 190 | 476 | 71 | 63 | |
Oct-42 | 29.4 | 235 | 502 | 20 | 43 | |
Nov-42 | 31.1 | 245 | 418 | 28 | 105 | 4 |
Dec-42 | 33.2 | 281 | 430 | 3 | 135 | 1 |
Jan-43 | 33.3 | 283 | 439 | 0 | 128 | |
Feb-43 | 35.0 | 302 | 519 | 0 | 43 | |
| Total | 30.8 | 2769 | 5200 | 480 | 560 | 5 |
9,014 US Merlins to end February 1943, which saw the last production of the Merlin 28 and 31, in March the final 44 single stage Merlins for the US and the start of Merlin 38 production.
3,016 Lancaster III times 4 engines, plus 1,054 Spitfire XVI and spares Throw in another 430 Lancaster X, 1,133 Canadian built Mosquitoes and the Australian ones (and Mustangs)
UK aircraft engine imports (all types), 2,704 in 1941, 3,145 in 1942, 9,441 in 1943, 11,327 in 1944, 4,528 January to June 1945.
The fundamental reason why production shifts took so much time was the cost and complexity of changing over, costs in money but also opportunity, what else could be done with the resources. Add retraining for the new type and stocking the spare parts system. Something that worked now was often preferred to something better tomorrow. For the western allies they also needed to have the aircraft they promised the USSR, which had its own preferences.
The "sudden overnight" decision by the Luftwaffe in the west to largely stop contesting front line area airspace in mid 1943, the appearance of Kamikazes, were way faster than any production system could react. So USMC fighter squadrons became carrier based.
In 1943/44 Bomber Command had Lancaster Finishing Schools, until then all training was on other types, in 1944 the 9th AF converted one of its P-51 groups to P-47 for a time. Those obsolete fighters could do as advanced trainers and operate in secondary theatres, like the F4F did.
The fighter bomber was making many multi crew light bombers obsolete. Hurricane or Blenheim, P-47 or A-20? The USN did publish performance tests for the F6F-3, -5 and F7F-1, -2 carrying a torpedo. The Fairey Firefly was not a good fighter compared with the F6F, but how about as a 2,000 pound bomber compared to the TBF/M?
Given the 1942 results it is unsurprising the USN made the dive bomber a required type but had trouble with replacement designs, so SBD production continued until August 1944 as the SB2A went nowhere, the SB2C had problems while the TBY was a 1945 aircraft, as was the BTD in a limited run. The Canadian SB2C lines: SBW started production in September 1943, the SBF (ignoring the prototype) in March 1944. In mid 1945 TBM production was about twice SB2C/SBW/SBF.
War Production Board, 778 PT boats November 1940 to August 1945, by year 10, 35, 127, 278, 204, 124.