During the Vietnam conflict, the United States Navy sponsored development of the silenced pistol for use by its SEAL teams. 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. Called the Mk22 Mod 0 by the Navy, the Hush Puppy had a slide lock to keep the mechanism closed and silent while firing. It fired a special green tipped 9mm parabellum projectile weighing 10.2 grams (158 grains that yielded a muzzle velocity of 274 m/s (900 ft/s), below the speed of sound. Use of standard supersonic ammunition quickly degrades the effectiveness of the silencer insert. With subsonic ammunition, an insert is good for about 30 rounds; wi