The SIG Sauer M17 and M18 pistols, or the military designation for the SIG Sauer P320, serve as the military’s current sidearms as they replace the older M9 pistols.
The M17 has a longer barrel and slide, while the M18 is more compact. The M17 will be issued to the army, and the M18 to the Marine Corps and to the Air Force. Time will tell as to how well the M17 and M18 will hold up, but so far the reception from service members has been very positive.
The P320 pistol is unique because it is a truly modular handgun. You can remove the gun assembly from the frame and then swap it out between pistols for convenience, which is one reason why the military decided to go with the weapon. Standard capacity is 17 rounds of 9mm.