WWII Telescope M6 1942

This scope measures 8-7/8" in length and reads: Telescope M6 NO 39127 E.K.CO. 1942 F.M.. I believe the E.K. Co. is for Eastman Kodak but I don't know what the F.M. is for. I have tried to research this and found two different answers as being for a 60MM mortar and a 37MM anti-tank gun. Condition is good showing honest age. The optics are good. Buyer to pay 6.00 shipping.