Did you know, in the mid and late 1980s, the U.S. Air Force issued a suppressed Beretta M9 to pilots in their survival kits? It was called the Knight’s XM9, as it was made by Knights Armament, but was more commonly known as the Hush Puppy. About 3,800 were ultimately made and sold to the USAF.

The name actually comes from an effort to sidestep the stigma around suppressor use during the Vietnam War. Special Forces determined a suppressed sidearm would be extremely useful on their operations, but there was resistance among the brass to issuing what was perceived as an assassin’s tool to troops in the field. So, the SEALs in Vietnam worked a little spin, and the S&W Model 39, a semi-auto 9mm pistol developed in the 1950s, with a suppressor became the Hush Puppy with the specific purpose of dispatching guard dogs. Other potential uses were simply ignored.

In the 1980s, the idea was revived, but this time, with the now-standard service pistol, the Beretta M9. The reason for wanting to include this suppressed M9 in Air Force survival kits was simple: a downed pilot practicing escape and evasion would only use their pistol in a defensive situation, meaning they were found by the enemy. If pilot could do so, neutralizing the immediate threat, with a lesser chance of notifying his buddies to his presence, there was a greater chance of survival. But this is one weird suppressor.

First, it’s not threaded. It attaches to a special barrel for the M9 with two large cuts near the muzzle via a proprietary device. Plus, it’s what’s called a wipe-based suppressor (more on that later).

That big silver contraption under the slide in Ian McCollum’s excellent video above doesn’t have anything to do with the suppressor directly, and it would have matched the finish of the gun on Air Force-issued pistols. It’s actually a slide lock that, instead of locking the slide back with the breech open, it locks the slide closed. This is simply to make the pistol quieter.

The Knight's XM9 Hush Puppy pistol.
The Knight’s XM9 Hush Puppy pistol. YouTube

If a suppressor works as intended and significantly quiets the report of the gunshot, the sound of the slide reciprocating and cycling, and gas escaping through the breech when the slide opens, actually makes up a lot of the noise that’s still heard, plus that distinct, metallic sound carries. If a suppressed shot has to be taken and concealment is a priority, this device turns the pistol into a single-shot, eliminating the noise of the cycling slide and back-pressured gas. Occasionally you’ll hear special forces folktales of operators pressing their thumb hard against the back of a slide when firing to accomplish the same thing.

This was also a feature on the Vietnam-era Model 39 Hush Puppy, but in that case, it also made the gun more reliable, as Browning-style designs with tipping barrels don’t always cycle very well with a heavy can hanging off the muzzle. Gun can’t jam if it can’t cycle. Modern suppressors overcome this with the addition of a spring loaded buffer that allows the barrel to move normally during cycling, independent of the weight of the suppressor.

The cuts on either side of the barrel extension work with a spring loaded quick-release device on the suppressor, which allows it to be quickly and easily attached with no risk of cross threading—because there are no threads. I imagine this would have been fairly easy to do with little training, even in darkness. It’s actually really ingenious, plus the top of the QD device acts as a rear sight that lines up with a bead front sight near the muzzle of the suppressor.

Inside the can, things are not what you’re used to. I said this is a wipe-based suppressor—that means the baffles are in the form of solid, polyethylene rubber discs. The bullet first enters a large expansion chamber, before it literally punches a hole through a total of eight “wipes”—rubber discs—stacked with spacers. This made for an exceptionally quiet shot. The wipes were under pressure that they resealed themselves to a degree after a bullet passed through—however, after about 20 rounds, there was pretty much a hole bored clear through, and the usefulness of the suppressor dropped dramatically.

This wouldn’t make any sense for recreational shooters, but for an emergency-kit gun, it did. The kit for the Knight’s XM9 Beretta included a case of additional wipes to replace the spent ones.

Knight’s Armament gained a good amount of suppressor experience with this design, and used it later in the 1990s developing the suppressor for what would become the H&K Mark 23 pistol, also used by special forces, though that suppressor was a much difference design.

In 2018, Knight’s Armament released the XM9 suppressor kits on the civilian market, so they aren’t exactly rare these days, but provide a cool glimpse back into earlier days of suppressor technology.