The Colt pistol was formally adopted by the Army on March 29, 1911, thus gaining its designation, M1911 (Model of 1911). It was adopted by the Navy and Marine Corps in 1913. Originally manufactured only by Colt, demand for the firearm in World War I saw the expansion of manufacture to the government-owned Springfield Armory.
Battlefield experience in the First World War led to some more small external changes, completed in 1924. The new version received a modified type classification, M1911A1. Changes to the original design were minor and consisted of a shorter trigger, cutouts in the frame behind the trigger, an arched mainspring housing, a longer grip safety spur (to prevent hammer bite), a wider front sight, a shorter spur on the hammer, and simplified grip checkering by eliminating the "Double Diamond" reliefs.
Those unfamiliar with the design are often unable to tell the difference between the two versions at a glance. No significant internal changes were made, and parts remained interchangeable between the two.