Why the USAAF gave up on the A-36 in favour of the P-47.

[Graham Boak]

The Allison Mustang was not preferred to the Merlin-engined one: it was preferred to the other types that were available for low-level fighter/recce, because of its longer range. The Merlin Mustangs were kept for use as fighters. If the RAF could have had all the Merlin Mustangs it wanted, some would have been free for FR roles.

[SteveB]

Tony

I, for one, am not certain whether the RAF’s policy on engine performance remained the same in 1943-44. Clearly in 1940-41 when the P-40 and the P-39 were being delivered and trialled in the UK, RAF planning for home-based units was focussed on the continuing expectation of an invasion and especially concerned about intercepting high-flying day bombers and their escorts. I agree that this was apparently a significant reason why both aircraft types were rejected for RAF Fighter Command although there were quite a few other important technical factors for both types.

I don’t think it was the case that in 1940-41 the RAF had clearly identified the potential of the low-level/TacR/fighter reconnaissance role even if ACC had. I don’t think it would have been possible at that time to allocate Hurricanes or Spitfires to ACC to develop that role but it did become possible to develop that role through the introduction of the P-40 and then the Mustang in ACC. By 1943-44 the Allison Mustang had proved itself in this role and, as I understand it, was competitive with the Merlin Mustang for speed at low altitude and, as Graham has said, with all other types available to the RAF as far as range was concerned. Perhaps the decisions were based largely on a “horses for courses” basis but it was certainly the case that in 1943-44 the RAF had a lot of unused Mk I airframes into which I assume it was not a simple task to drop a Merlin engine and apparently there were no replacement Allison engines.

My understanding is that in the planning for Merlin Mustang production it became clear at an early stage that there was never going to be enough airframes or engines to meet all the expectations the allied air forces had for the aircraft. As you say, MAP may have been able to specify Merlin Mustangs “from the get go had the RAF wanted them” but the BAC files do not confirm that they would have been allocated to the RAF. The BAC files show that, in the process of agreeing the bi-annual planning protocols that under-pinned the lend-lease allocations, the BAC went into negotiations with expectations (from RAF/MAP?) that they were not able to agree with the Americans and the reviews of the six month protocols show that the final allocations of Merlin Mustangs to the British were usually less than had been previously agreed in those protocols.

I think the engine in the XP-40F was a Merlin XX?

Steve