DeepSea wrote:

snip

That would explain the British complaint with the early P-51's lack of
high altitude performance. Based on the information I had, I (apparently
incorrectly) assumed that there was no need for a fighter with good high
altitude performance - I thought that most of the action during the BoB
was down low where the early P-51 was actually pretty capable.

The Mustang didn't arrive 'til well long after the Battle of Britain, so the
point is moot anyway. Requirements would have moved on.

Graham