+12 boost

[reflected]

Right now we seem to have 1939 Messerschmitts, Spitfires, and Hurricanes.

Apart fro mthe lack of Rotol Constant speed prop on Spitfire MKIa-s, there's something else: 100 octane fuel and +12 boost:

Trials were successfully carried out in October 1939 to increase the power of the Spitfire's Merlin II and III engines by raising the manifold pressure to +12 lbs./sq.in. 26 Air Ministry A.P.1590B/J.2-W. dated 20 March 1940 gives official notice that "The emergency use of higher boost pressures up to +12 lb./sq. in. is now permitted for short periods by operation of the modified boost control cut-out". 27 Also during February and March 1940 Spitfire and Hurricane Squadrons were converting their aircraft over to 100 octane fuel, which made possible an increase in engine power by raising the boost to +12 lb/sq.in.. 28a 28b 28c 28d 28e 28f 28g 28h 28i 28j 28k 28l 28m 28n 28o 28p 28q 28r 28s Combat reports show that +12 lb boost was used by the Spitfire (and Hurricane) squadrons during their first combats with the Me 109 E in May 1940 while covering the Dunkirk evacuation. 29 30 Hurricane Squadrons based in France during May of 1940 were also employing +12 lbs/sq.in. boost in combat. 31 31b

Apparently this was used even during Spring 1940, when the RAF still used de havilland props.