At the beginning of the 20th century, the United States Army had a problem. Its soldiers were fighting in the Philippines, and many officers felt that the standard-issue .38 calibre revolver lacked the power to stop a determined attacker at close range.
In 1904, Captain John T. Thompson and military physician Louis La Garde conducted a series of tests to determine the appropriate calibre for the army's new sidearm. Their conclusion was clear: it had to be at least .45 calibre.
The army then launched a competition. Among the designers who participated was John Moses Browning, one of the greatest names in the history of firearms, who submitted a semi-automatic pistol manufactured by Colt and chambered for a cartridge designed specifically for it: the .45 ACP.
The ultimate test wasn't just about how well it fired. It was about how much it could withstand. During the trials, Browning's pistol fired six thousand rounds without a single malfunction, while its competitor suffered numerous breakdowns. The result was decisive, and on 29 March 1911, the U.S. Army adopted the new pistol as the M1911. In the mid-1920s, it underwent a series of modifications and was designated the M1911A1.
But the .45 calibre wasn't going to stay confined to a pistol.
The same Thompson who had championed that calibre was now thinking about something different. During World War I, he envisioned a lightweight automatic weapon that used pistol ammunition and could "sweep" a trench at close range. In 1916, he founded the Auto-Ordnance company to develop it, and he gave the result a name that didn't exist until then: submachine gun. The war, however, ended before his weapon reached the European battlefields.
Thompson had to wait.
The weapon was released to the civilian market in 1921 and initially encountered a very different setting from the one its creator had imagined. During Prohibition, criminal gangs in cities like Chicago adopted it, and the press began calling it the Tommy gun or the Chicago Typewriter. The St. Valentine's Day Massacre of 1929 cemented that image.
Its military destiny came later. The U.S. Navy adopted the Model of 1928, and the Army incorporated the Thompson in the late 1930s. With World War II came large-scale production: first the M1928A1, which could use drum or straight magazines, and from 1942 the M1 and M1A1 versions, simplified for faster production and designed only for straight magazines, which were more reliable in the field. Twenty-five years after its conception for the trenches, Thompson's weapon finally went to war.
And then the circle was complete. Browning's pistol and Thompson's submachine gun shared the same cartridge. The .45 ACP round that fed the pistol in an officer's holster also fed the automatic weapon of the soldier advancing beside him, in Europe, in the Pacific, and, years later, in Korea.
The submachine gun eventually gave way to more modern weapons. The pistol endured much longer. It survived two world wars, Korea, and Vietnam, and the U.S. armed forces amassed some 2.7 million units. When it ceased to be the standard-issue sidearm in 1985, seventy-four years had passed since that 1911 decision.
It had all begun with a simple question about the calibre of a pistol. The answer ended up arming several generations of soldiers.
