The primary modification was the use of a folding metal stock which reduced the length of the weapon by ten inches. Although the stock added a quarter of a pound to the weight of the carbine, the small size was vital for paratroopers and other soldiers who needed a more compact weapon.
Approximately 150,000 M1A1 carbines were built during World War II by Inland Manufacturing Division (GMC).
The M1A1 carbine, with its distinctive folding stock, is seen being used by the paratroopers in Neuville and Ramelle. 36 carbines (a mixture of M1 and M1A1s) were used during the movie's production.