The danish police uses the H&K USP Compact 9mm
Great stopping power!
Point of ballistic realities. The H&K USP is a fine firearm, but the 9mm cartrige is a poor stopper. There are fewer and fewer U.S. agancies still using it. It's nothing more than a .38 special; both in bullet weight/diameter and velocity.
There's an elusive formula for weight/diameter/velocity that equates to stopping power. (not killing power, but where the victim "stops" being a threat)..
Years ago, Evan Marshall set out digging through YEARS of shooting data in order to document the best, "One shot stop" bullet. What he came up with was:
125grain .357Magnum @ 1400fps
Because of the 9mm craze of the 80's (something like 80% of departments tried the 9mm) ... the data was skewed, slightly improving the 9mm reputation, but when the dust settled, the .357Magnum was still way ahead (something like 97% one-shot stops).
Unfortunately, that round is a revolver only. There are some hybrid caliber semi-autos out there, like the 357Sig, but they're hardly mainstream and police departments shy away from them.
.44Magnum and 10mm are more powerful on paper, but that power never translated into stopping power in the real world. Mostly due to over-penetration (wasted energey not used up in the target).
.40S&W and .45ACP are the best bets in semi-auto pistols, though the .45ACP isn't much better than the 9mm for stopping power.