Heckler & Koch introduced the UMP submachine gun as a successor to the MP5, with a particular focus on American law enforcement agencies (hence its initial development in .45 ACP). The UMP never has come close to the popularity of the MP5; it is a very basic polymer molded simple blowback SMG, albeit a hammer-fired, closed-bolt one. However, H&K did release a civilian version of it in semiautomatic only; the USC. These were initially made in a grey color like the SL-8, but demand was substantial enough to prompt continued production in black.

Compared to the UMP, the USC has a neutered magazine well that fits only proprietary 10-round magazines, a thumbhole type fixed stock, and a heavy 16" barrel. I suspect a majority of the demand for the USC comes form people planning to swap out all these elements to properly clone the UMP...