The Mk 22 is a modified Smith & Wesson M39 pistol with a silencer, but it's mostly known as the "Hush Puppy."
During the 1960s, the Navy SEALs were just starting to develop their clandestine techniques that would eventually turn them into one of the finest fighting forces in the world. Being special operations commandos, they had their pick of conventional and non-conventional military weapons.
One of those was the M39. But after a few runs in the field, the frogmen started asking for modifications, which resulted in a longer barrel threaded at the muzzle to accept the screw-on suppressor, among other modifications.
"We'd go into these villages at two or three o'clock in the morning, and the dogs and ducks raised all kinds of kain [noise]," said former Navy SEAL Chief James "Patches" Watson in the video below. "We needed something to shut them up without disturbing the whole neighborhood."
The gun was fantastic for silencing noisy dogs, hence its nickname. (Editor's note: please don't kill dogs.)
American inventor, Hiram Percy Maxim created the first commercially successful firearm suppressor in the early 1900s, giving way to the quietest gun on the battlefield.
Ironically, his father, Hiram Stevens Maxim, was the inventor of one of the loudest — the Maxim Gun. This weapon was the first fully automatic machine gun, according to the Encyclopedia Britannica.
Maxim Jr.'s suppressors were popular in the 1920s and 30s among shooters and sportsmen before being adopted by the Office of Strategic Services — the predecessor of the modern CIA — during World War II. The next use by the American military were by the Navy SEALs, according to this American Heroes Channel video:
American Heroes Channel, YouTube