The Mk22 Mod 0 "Hush Puppy" is a compact semi-automatic pistol.Nicknamed the "Hush Puppy" because of its intended function of taking out sentries and enemy watch dogs, this modified version of the steel framed Smith & Wesson Model 39 pistol was put to other clandestine uses as well. the Hush Puppy had a slide lock to keep the mechanism closed and silent while firing. It fired a special green tipped 9mm parabellum.n 1964, the Mk22 was used by Naked Snake during the Virtuous Mission, which utilized an even more specialized ordnance in the form of 9mm tranquilizer rounds, capable of putting a target to sleep for a short time. It was a test model for the Mk22 that was under development in the U.S. Navy, modified by the CIA to utilize tranquilizer darts. In terms of operation, magazine capacity and performance, the Mk22 represented by FOX Unit captures the ideal of a "perfect pistol for a sneaking mission."