[Kurfürst]

Originally Posted by Seadog

The Merlin XX was given official approval to use 12lb boost for combat in MS gear in Nov 1940, but the engine was cleared for 12lb boost/3000rpm for TO right from the beginning, and so was available to any pilot who cared to use it during combat.
http://www.wwiiaircraftperformance.o...s-10june40.jpg
http://www.wwiiaircraftperformance.o...xx-15nov40.jpg

Approval for 14 and then 16lb boost was added later, along with the appropriate boost override modifications.

GP! The bottomline though, the initial combat rating was clearly +9 (until november).