This compact handgun was designed in Germany in 1989. The Variant used in all games is the USP compact chambered to use .45 ACP rounds, which has a smaller and lighter design in comparison to a regular USP. The weapon is used by Veteran/expert members of Freedom, Loners, and Mercenaries, in most games.
In Shadow of Chernobyl, the UDP is heavily employed by veteran and Expert Freedom members as their sidearm and sold exclusively by Skinflint. The USP Compact has significantly better firing rate compared to other .45 caliber pistols and very light, weighing less than 1.00kg.
However the UDP seems to be susceptible to jamming, which makes it slightly unreliable in extended firefights.
In Clear Sky, the UDP Compact is used by expert members of Freedom and some experienced members of the Mercenaries and veteran Loners . It is still very light, weighing at less than 1.0kg and its magazine can be expanded by 4 bullets to have a total of 12 bullets per magazine. It has a better firing rate than other .45 caliber pistols and retains a degree of accuracy and power, though not as powerful nor as accurate as a Kora 919. Most technicians can upgrade the weapon and it is sold only by Ashot, though you can salvage one early in the game while fighting the mercenaries in the Dark Valley. You can only buy this pistol from Ashot after attaining a friendly reputation with Freedom.
In Call of Pripyat, the UDP Compact is used by Mercenaries, Loners, Freedom and sometimes even Zombified Stalkers. Nimble can sell you a unique USP called March which used to belong to a mercenary Wolfhound. It is one of the pistols that can be modified to have a new firing mode – in this case, fully automatic. It is the only .45 caliber pistol with this upgrade.