You're forgetting that in WWI and WWII the US sold many ships (not ships of the line but slightly older ones as well as weapons, ammo, and other equipment to other allies, and Germany but that's besides the point. Germany and Japan didn't use each others planes because of logistics mostly. I'm sure they would have if possible.
The US even sent pilots over to England before the war started to serve in the RAF. (no, not Red Army Fighter). So CAN allies share weapons/ships? sure, but make SURE that there is a forum post/thread about it.