Does anyone know anything about such a cartridge?

The case is a bottle-necked, "rimless" type, unlike the 37mm round for the dinky anti tank gun and the secondary armament in the M3 medium tank, etc..

Actually, the rim, at 2" / 51mm. is a bit larger than the rear of the case body; more of a "semi-rimmed" style.

Case length is 220mm / 8 11/16".

I only have a fired case, no projectile. In profile, it looks like a "real-man's" .30-06.

The head-stamping is VERY faint and there are coarse lathe-tool marks across the head. Probably WW2 "accelerated production.

US Navy, perhaps?. The only other 37mm that springs to mind is the one fitted to the P-39, which were operated in the area where this originated.