[Graham Boak]

Re Hurricanes: the armour plate behind the pilot was there on the standard aircraft, so would not be counted in any deltas. If you seriously doubt the presence of any other armour, just look at the different shape of the radiator on the Mk.IV. In all fairness the Mk.IV is certainly the least well described of all the Hurricane variants, but if you do some more research you will track down details. There never was, however, any suggestion that its armour matched the amount present on the Il 2. Armoured and unarmoured is not a simple yes/no switch, but covers a wide spectrum of possibilities.

I have checked against Shore's description on the desert Hurricane Mk.IId. Nowhere does it state that the the armour was in existence and deliberately taken out because of RAF instructions, as you suggest. He states that the design did not have it, which is well known. I suggest it is ambiguities in the word "omission" that has mislead you. It was omitted for the same reason as a cigar lighter - because it was not specified and not available. I grant you that it would have been more useful than a cigar lighter, but as Shores points out it would also have penalised the already poor performance of the tropicalised Mk.IId. Life is full of compromises, and combat aircraft design has many.

I believe that the P-39 could have been turned into a reasonable GA aircraft - as good as the Spitfire, say. Why anyone should bother, given the alternatives, is more difficult to imagine. Despite dubious unproven claims of survivability, I still see no good reason why this slower less-powerful type, with its inadequate payload and limited firepower, should be preferred to the more rugged and capable Typhoon for the GA role.

The forward radiator does not seem to have been any penalty in belly landing, though it was in ditching. The Typhoon was very tough, with a rigid cockpit and pilots survived very heavy landings. One drawback was in the event of overturning, where the bubble-hood version lacked a roll-over bar or pylon and several pilots suffered severe spinal injuries or broken necks. I am very surprised that this point was not picked up early in service.

Jukka: your comments are entirely true from the viewpoint of interesting and exciting engineering. Wonderful engines. However, Fedden's efforts in that direction meant that an 1300hp radial (the Hercules) was not available in the same timescale as the Merlin, and the 2000hp Centaurus missed the war altogether (apart from a few Warwicks). With all the benefits od hindsight, I suggest that the RAF, particularly its ground-attack units, could have been better served with clumsier draggier engines of similar power available two years or more sooner. Other nations managed perfectly successful power units without the theoretical attractions (but very severe development problems and delays) of the sleeve valve. It is that horribly depressing situation of compromises again. The war came just too soon for the sleeve valve.