The 1911A1 is a semi-automatic pistol designed by John Browning and adopted by the United States military in 1924 as an improved version of the original M1911. It is chambered for the .45 ACP cartridge and features a single-action mechanism, which means the hammer must be cocked before firing. The design is known for its reliability and stopping power. The 1911A1 includes several enhancements over its predecessor, such as a longer grip safety and improved sights. It has become a popular choice for both military and civilian use, often praised for its accuracy and customizable options. The pistol remains a significant part of firearm history.