grenade and M18 smoke grenade. Many units are supplemented with a variety of specialized weapons, including the M249 SAW (Squad Automatic Weapon), to provide suppressive fire at the squad level. Indirect fire is provided by the M320 grenade launcher. The M1014 Joint Service Combat Shotgun or the Mossberg 590 Shotgun are used for door breaching and close-quarters combat. The M14EBR is used by designated marksmen. Snipers use the M107 Long Range Sniper Rifle, the M2010 Enhanced Sniper Rifle and the M110 Semi-Automatic Sniper Rifle. Crew-served weapons The army employs various crew-served weapons to provide heavy firepower at ranges exceeding that of individual weapons. The M240 is the U.S. Army's standard Medium Machine Gun. The M2 heavy machine gun is generally used as a vehicle-mounted machine gun. In the same way, the 40 mm MK 19 grenade machine gun is mainly used by motorized units. The U.S. Army uses three types of mortar for indirect fire support when heavier artillery may not be appropriate or available. The smallest of these is the 60 mm M224, normally assigned at the infantry company level. At the next higher echelon, infantry battalions are typically supported by a section of 81 mm M252 mortars. The largest mortar in the army's inventory is the 120 mm M120/M121, usually employed by mechanized units. Fire support for light infantry units is provided by towed howitzers, including the 105 mm M119A1 and the 155 mm M777. The U.S. Army utilizes a variety of direct-fire rockets and missiles to provide infantry with an Anti-Armor Capability. The AT4 is an unguided projectile that can destroy armor and bunkers at ranges up to 500 meters. The FIM-92 Stinger is a shoulder-launched, heat seeking anti-aircraft missile. The FGM-148 Javelin and BGM-71 TOW are anti-tank guided missiles. Vehicles U.S. Army doctrine puts a premium on mechanized warfare. It fields the highest vehicle-to-soldier ratio in the world as of 2009. The army's most common vehicle is the High Mobility Multipurpose Wheeled Vehicle (HMMWV), commonly called the Humvee, which is capable of serving as a cargo/troop carrier, weapons platform and ambulance, among many other roles. While they operate a wide variety of combat support vehicles, one of the most common types centers on the family of HEMTT vehicles. The M1A2 Abrams is the army's main battle tank, while the M2A3 Bradley is the standard infantry fighting vehicle. Other vehicles include the Stryker, the M113 armored personnel