The MGS's low profile turret has a small silhouette, is stabilized and mounts a 105mm M68A1E4 rifled cannon with a muzzle brake and an autoloader. The vehicle is primarily outfitted to support infantry combat operations. While it could take on some of the roles of tanks, it is not designed to engage in combat with tanks. The MGS can store 18 rounds of main gun ammunition, 8 in the autoloader's carousel and an additional 10 in a replenisher located at the rear of the vehicle. It has a rate of fire of six rounds per minute. The MGS's 105 mm cannon can fire four types of ammunition: the M900 kinetic energy penetrator to destroy armored vehicles; the M456A2 high explosive anti-tank round to destroy thin-skinned vehicles and provide anti-personnel fragmentation; the M393A3 high explosive plastic round to destroy bunkers, machine gun and sniper positions, and create openings in walls for infantry to access; and M1040 canister shot for use against dismounted infantry in the open.
Crew amenities
Because the vehicle was originally designed without air conditioning, crews are given individual cooling vests that circulate cooled water from outside the vehicle to the garment. Vehicle computers still overheat regularly. The large weapon station and relatively smaller hatch can make emergency exits difficult. Because the main cannon is separated from the crew compartment it is possible for the crew of an MGS to encounter a stoppage in the heat of battle and not be able to clear it without disembarking from the vehicle. All MGS Stryker platforms have since been upgraded with A/C units.
Organization
The U.S. Army allocated nine Mobile Gun Systems to a battalion. There were 27 Mobile Gun Systems per Stryker Brigade in 2013, but later the Army cut the number per brigade to 10. The Army bought 142 Mobile Gun Systems in total; 3 were lost in combat. A three-vehicle MGS platoon operates organic to a Stryker infantry company, with one MGS in support of a Stryker infantry platoon. As of May 2017, a Stryker Brigade Combat Team is equipped with three platoons of MGS Strykers and three platoons of ATGM Strykers in its weapons troop.
Following the end of the Cold War some theorists believed that the existing suite of U.S. armored vehicles, designed largely to fight Soviet mechanized forces in Europe, were not well suited to the lower-intensity missions U.S. armed forces would be tasked with. This led to the development of a new armored fighting vehicle designed for lower-intensity combat, rather than large-scale battle. Canada had liquidated about half of its fleet of Leopard 1s in the early 2000s, with the intention of replacing them with the Mobile Gun System, but the decision was reversed. Full-rate production has been indefinitely deferred as of 2012. In late 2013, the U.S. Army began seeking to reintroduce an airdroppable mobile airborne protected firepower platform to provide fire support for air assault forces, a capability that had been absent since the retirement of the M551 Sheridan in 1997. General Dynamics initially considered modifying the wheeled Stryker MGS to meet the requirement, but the company instead developed the tracked Griffin light tank technology demonstrator as its offering for the Mobile Protected Firepower platform, which was unveiled in October 2016.
