The Heckler & Koch USP, short for Universal Self-loading Pistol, was a line of semi-automatic handguns manufactured by Heckler & Koch.
The USP employed specially molded polymers to reduce its weight and had mechanical recoil reduction technology that made it a favorite for combat and undercover work. (24: The Ultimate Guide)
The USP Tactical was a variant with many special features, including rear target sight adjustment, an O-ring barrel that allowed the use of a KAC suppressor, and an ambidextrous magazine release that allowed the operator to eject a spent magazine without having to readjust their grip. The Mark 23 USP was a lighter version of the Tactical that lacked some of its more advanced features. (Operation Hell Gate)
Before Day 1
During the hunt for Frank Hensley, Jack Bauer borrowed a Mark 23 USP from Georgi Timko. He later used it atop Hell Gate Bridge to stop Hensley and Omar Bayat from shooting down a CDC charter flight containing a strain of the 1918 influenza virus. (Operation Hell Gate)
During the hostage situation at the Chamberlain Auditorium, Secret Service agent Craig Auburn gave a .45-caliber USP Tactical to Vice Presidential aide Adam Carlisle in case they were found by the terrorists. (Trojan Horse)
A former Serbian soldier loyal to Erno Tobias used a silenced USP Tactical to kill a security guard at CTU New York so he could plant a bomb on the building's microwave tower. Later, Vernon Greene and Farshid Amadani, two of the terrorists involved in the Kurmastan suicide bombings, also used USPs in the commission of various crimes. (Collateral Damage)
Day 1–Day 8
Sometime around Day 3, Jack Bauer switched from the Sig Sauer P228 to the 9mm HK USP Compact for his sidearm of choice, and relied on it on various missions throughout the next decade. ("Day 3: 1:00pm-2:00pm", many more) By Day 9, Bauer instead used the P30, another Heckler & Koch pistol. ("Day 9: 9:00pm-10:00pm")
- For the full list of appearances in 24, see Handguns on 24.