M17 / M18

Tim Butler designed the firearm between 2015 and 2017. Developed by SIG Sauer, Inc. in Newington, New Hampshire, the handgun is a derivative of the P320 model. The manufacturer modified the design to compete in the United States Army's Modular Handgun System trials, also known as the XM17 Procurement. On January 19, 2017, the United States Army selected the modified P320 as the winner of the competition, subsequently designating the full-size version as the M17 and the carry-size version as the M18.

The firearm is a short recoil-operated, semi-automatic handgun. It features a slide cut-out for the attachment of a reflex sight, an ambidextrous thumb safety, and a loaded chamber indicator. To improve maintenance and reliability, the slide sub-assembly captures small components during disassembly, and a trigger "mud flap" prevents foreign debris from entering the action. Steel components are treated with a physical vapor deposition corrosion-resistant finish. Specialized spanner screws are utilized on the chassis to restrict disassembly beyond basic field stripping by non-armorer personnel. The weapon incorporates self-illuminating tritium sights for low-light environments, an integrated accessory rail, and compatibility with a standardized suppressor conversion kit. Factory acceptance includes a thirteen-round test-firing sequence. The handgun is optimized for Winchester-manufactured ball and jacketed hollow-point ammunition, designated as the M1152 and M1153 respectively.

Entering service in 2017, the handguns were adopted by the United States Army, Navy, Marine Corps, Air Force, and Space Force to replace the Beretta M9 and other secondary firearms. The weapons saw deployment in the War in Afghanistan and the Global War on Terrorism, with distribution extended down to the squad and fireteam leader level. The Kosovo Security Forces also adopted the system. In 2025, the Air Force paused operations of its M18 fleet for safety inspections following a fatal discharge at Francis E. Warren Air Force Base, resuming service after addressing component issues in a subset of the inventory. Standard military variants include the full-sized M17 and the compact M18. Special variants include four aluminum-framed ceremonial models for the Tomb of the Unknown Soldier, engraved with symbolic motifs and fitted with historical wood grips. SIG Sauer also released civilian versions, including the P320-M17, the P320-M18, and a limited-edition M17 Commemorative built to military specifications.