I recall reading of an incident in the Western Desert when a British officer fired at a very low-flying Bf 109 with his .38 revolver. One bullet hit a fuel or coolant line (I forget which) which eventually caused the plane to crash-land. As a PS, both the officer and the pilot survived the war and met afterwards.
There was also an incident discussed on the Key Publishing site a few months back concerning another British officer who fired on a twin-engined German plane with a (presumably unofficial) 9mm pistol, and again brought it down.
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