Serial number blocks assigned by the government:
M1 Carbines 545,616 (Underwood, did not make the M2, M3, T3, or M1A1 Carbines) Approximately 545,616 total Carbines were made by Underwood: About 8.9% of M1 Carbines made. Average Cost to Government per completed rifle, $47.82.
Main plant location: Hartford, Connecticut.
' (a U with two periods on each side, in the center) Main Manufacture and identification codes: '.
