I have been asked how we can be sure the lost plane was a P-38. Allison engines, for example, were also used on A-36s, P-51As, P-40s and P-39s and P-63s. Here is my thinking on the matter but I would be interested what others think. P-38s had two Allison engines. They turned in opposite directions. Armament consisted of four 50 cal machines guns and one 20 mm cannon, all mounted in the nose.
Starting with the serial numbers of the unknown. We have for the guns: 1190382, 1190815, 1294465 and 120206 and for the Allison engine: A-047489.
We have identified in MACRs a series of Savage Arms M2 50 cal machine guns. They have numbers on both sides of 1190382 and 1190815. The planes with these guns were all P-38J-15-LOs and all were manufactured at the same time. Their serial numbers range from 44-23059 to 44-23208.
Gun 1294465 appears to be a M2 50 CAL machine gun manufactured by Buffalo Arms. I have found 1294418 in a MACR identified as a Buffalo Arms M2 machine gun for example.
120206 appears to be a 20mm cannon, as I have found 120207 identified as a 20 mm cannon.
20 mm: 120259, 120231
https://www.fold3.com/image/28697341 (MACR for a P-61)
20 mm: 120207 :
https://www.fold3.com/image/29250882?terms=42%5C-5583 (MACR for a P-61)
I think this series of 20mm cannons was made by International Harvester.
Now A-36s, P-51As and P-40s only carried machine guns, not 20 mm cannons. So I think they are ruled out.
P-39s did have a cannon. The original models had 20mm cannons but the later models had a 37mm cannon. The Italians did operate P-39s over the Balkans late in the war. From a wikipedia article (so consider the source):
“12° Group's P-39s flew their first mission over Albania. “Concentrating on ground attack, the Italian P-39s proved to be suitable in this role, losing 10 aircraft between 4 November and 3 December 1944”.
“The 4°*Stormo*pilots flew many effective ground attack missions on northern*Yugoslavia, losing only one more P-39, for engine failure in*Sarajevo*area, on 2 April 1945.”
And of course, the Russians had received P-39s and P-63s as lend lease. The P-63s also had 37mm cannons.
The P-39 model both the Italians and Russians were using, the P-39Qs had the 37mm cannon. Also the Russians sometimes removed the 50 cal M2 in the wings and flew with only two 50 cal in the nose along with the 37mm cannon. The P-63s flown by the Russians also had a 37mm cannon.
I think the fact that a 20 mm cannon was found pretty much rules out the P-39s and P-63s, even though they did have Allison engines.
The models of Allison engines used in P-39s and P-63s were different than the models of Allison engines used in P-38s. The unknown had serial number A-047489. That serial number is for a V-1710 , -89 or -91 engine. (The two engines on a P-38 turned in opposite directions and the I think the -89 or -91 were those two versions of the same engine.
The Allison engine models in the P-39Qs were V-1710-85s and in the P-63 were were V-1710-117s.
So the Unknown had a P-38 type engine and not a P-39 or P-63 type of Allison engine.