At its core, the M3 Carbine was nothing more than the M2 Carbine form (detailed elsewhere on this site) with its upper section of the receiver modified to accept an InfraRed (IR) sight mounting to allow for engagement, at range, in low-light-level/night time conditions. It lacked the open iron sights of the earlier M1 and M2 marks as a result but all other functions of the gun were faithful to the originals. Various IR sights were developed during the course of the M3's operational existence and these scopes designated simply as the "M1", "M2", and "M3".
Again the engineers of the Inland Division of General Motors were charged with getting more out of the M1/M2 Carbine family so design work began in 1940 leading to limited production beginning in late-1944, early-1945. This, in turn, led to the developmental designation of "T3" being assigned to the new carbine. The earliest scope in play became the M1 "sniperscope" which was known developmentally as the "T120". Effective range of the modified M2/T3 was now out to 200 to 300 yards in low-level-light conditions, aided primarily by the installed scope.
Between 2,100 and 3,000 M3 Carbines were produced by Inland but the gun series never existed, at least officially, beyond their few-thousand-strong semi-prototype forms. The series did see limited circulation towards the end of World War 2 (1939-1945), and were actively fielded at the Battle of Okinawa, but wider-spread service was had during the Korean War (1950-1953). It saw some service in the Vietnam War (1955-1975) as well with special forces elements but, in time, was surpassed by more potent sniper solutions of the Cold War period.