During World War II, the Office of Strategic Services (OSS) was responsible for coordinating espionage and other secretive missions behind enemy lines. As a result, this organization developed some fascinating weapons and gadgets — often the sort of thing you'd expect to see in a James Bond film. These included covert firearms, explosive devices, and poisons designed to eliminate high-value targets.
One weapon developed by the OSS was known as the Stinger, and resembles the size and shape of a pen. In actuality, it was a covert gun that fired a .22 Short cartridge. The OSS Stinger was designed for single use and sealed around the cartridge, so once it had been fired, it was disposed of immediately.
Several variants of the Stinger were developed throughout the war, with reinforcements made to the chamber and firing mechanism to reduce the risk of misfires (and damage to the shooter's hand). In the following video, Ian McCollum of Forgotten Weapons examines three variants of the Stinger pen gun and discusses its history in greater detail: