The genesis of the B&T USW was a two and a half hour car ride home from a youth hockey game, when Karl Brugger and a friend were thinking about how to improve police effectiveness with handguns. What would make a handgun more accurate in practice? Clearly a red for and a shoulder stock. So how does one add those elements to a pistol while maintaining easy carry in a service holster? The answer was the USW.

The first prototypes were built on AT-84 Sphinx pistols (a Swiss-made copy of the CZ75). The first production run used Sphinx components, but with newly made frames and slide that incorporated cocking surfaces forward not he slide and an extension off the frame to mount the side-folding stock and Aimpoint Nano optic. Only a few of these were made, as the project was never all that popular.

Other experiments included conversions for other pistol models, with the SIG P320 being the most practical. Clamp-on conversion kits were made for guns like the CZ P10, Walther PPQ, and Glock.

Perhaps the most influential outcome of the project was the optic. Aimpoint originally developed the Nano as B&T's request, but in the original form is was not nearly as reliable as Aimpoint desired. It was iterated and ruggedized (and renamed to avoid a lawsuit over the Beretta Nano pistol) and became the very successful Aimpoint Acro.

My 2022 Desert Brutality match with a USW-320:
https://forgottenweapons.vhx.tv/videos/evaluating-the-modern-stocked-pistol-usw-320-at-desert-brutality-2022