The M1A1 carbine was officially standardized in May 1942, and the first deliveries began in October.
The so-called 'First Contract' carbines were shipped between October 1942 and October 1943, with approximately 71,000 M1A1s delivered during the period. Serial numbers ranged approximately from 42,000 to 850,000.
Barrel dated 12-42; this M1A1 carbine is serial numbered 123829.
One of the early ones.
https://www.milsurps.com/images/impo...DSC02018-1.jpg
David