Developed during WWII, the M3 was named a "sniper scope" in official nomenclature to obscure its true function as an early infra-red night scope capable of spotting targets at over 100 yards and detecting other IR-sources up to a mile away. Mounted on an M1 semi-automatic carbine, the scope could be used by night sentries to detect incoming sneak attacks and direct outbound machine gun and rifle fire with tracer rounds. Overall dimensions are 16 3/8 inches long and 10 inches tall with a 5 3/4 inch diameter infrared emitter on top and Army Corps of Engineers/American Optical Company markings on a sticker on the rear of the emitter and a panel on the right side of the base. In a green painted hardwood case with white stenciled "U.S./SNIPERSCOPE/INFRARED/SET NO.1, 20000 VOLTS" on top of the lid, another Army Corps of Engineers/American Optical tag on the inside, 1 battery carrier and a pistol grip/power switch assembly.