Maxim Gun, 1883
Sir Hiram Maxim was an American inventor who emigrated to Europe. His creations included fire sprinklers and steam-powered aircraft, but his most successful invention was the Maxim fully automatic machine gun. The weapon was recoil-operated, meaning that it didn't need to be cranked by hand to load new cartridges, as the Gatling gun did. Instead, the force of the recoil ejects the spent cartridge and loads a fresh one. The Maxim proved far more effective and reliable than competing weapons. Both sides of combatants in World War I used versions of the gun; it stayed in service into the 1960s.
Colt M1911, 1911
John Browning developed a new .45 cartridge with improved stopping power in 1904. Later, he built a gun around it. Adopted in 1911, the M1911 earned plenty of respect and caused plenty of fear during decades of service, through two world wars and in Korea and Vietnam before it was replaced by the 9-mm M9 Beretta. The M1911 earned a reputation for accuracy and reliability. Although its replacement has twice the magazine capacity and is less prone to accidental discharge many still prefer the M1911.