On 29 March 1911, the Secretary of War approved the Colt Caliber .45 Automatic Pistol. It would become the longest serving handgun in US military history. And one of the most enduring handguns in US history.
The gun, designated M1911 and now often called just “1911” in civilian hands, was adopted after 12 years of the military considering the use of an “automatic” handgun and the inventor, John Moses Browning, had worked on this project for 16 years as he had designs, and maybe prototypes, back in 1895!
In 1911, the right combination of design, capability, and reliability was proven in a 6000 round endurance test.
Amazingly, the prototype still survives. (The photo is from M1911 forum.)
Some more history:
https://ambivalentskeptic.wordpress.com/2011/03/03/m1911-history-on-this-day-03-march-1911/
https://ambivalentskeptic.wordpress.com/2011/03/15/m1911-history-on-this-day-15-march-1911/
https://ambivalentskeptic.wordpress.com/2011/03/20/m1911-history-on-this-day-20-march-1911/
And Chris Byrne has a good post (with a nice photo):
http://anarchangel.blogspot.com/2011/03/happy-1911-day.html