Of all the sins one can lay at Martin Caiden's door, I'm not sure "forked-tail devil" is down to him.
I'm looking at a copy of "AAF Manual 51-127-1 Pilot Training Manual for the P-38 Lightning", apparently published 1 August 1945, which claims "the men of the Luftwaffe" called the P-38 "The Forked Devil."
No citations are provided...