These shell casings are for the Japanese 5cm boat gun but is really 47mm diameter. The Japanese bought the gun and ammunition from the British prior to WWII, shell cases are marked EOC (Elswick Ordnance Company) and then some Japanese inspection marks. Later they manufactured their own ammunition. One of the case's is all Japanese mfg the other British mfg, I have been told the all Japanese manufactured cases and projectiles are quite difficult to find.