U.S. Army itself is led by the chief of staff of the Army and vice chief of staff of the Army, both generals who are advised by the sergeant major of the Army. The Army's primary responsibility is to conduct prompt and sustained land combat as part of the joint force. Army landpower focuses on destroying an enemy's armed forces, occupying its territory, and breaking the will of an adversary. The five core competencies of the Army are: Prompt and sustained land combat Combined arms operations: Combined arms maneuver and wide area security Armored and mechanized operations Airborne and air assault operations Special operations Set and sustain the theater for the joint force Integrate national, multinational, and joint power on land Infantry The Infantry Branch forms the core of the service's land combat power. U.S. Army infantry are generally equipped with the M4 carbine and M249 light machine gun, which will be replaced by the XM7 rifle and XM250. Infantry is a core part of the Army's Brigade Combat Teams. The most numerous variant, the Infantry Brigade Combat Team, comprise light infantry battalions who fight on foot. Infantry Brigade Combat Teams of the 82nd Airborne Division are air assault capable, with infantry soldiers being transported by U.S. Army Aviation UH-60 Black Hawk and CH-47 Chinook helicopters. Infantry Brigade Combat Teams of the 11th Airborne Division, 82nd Airborne Division, and 173rd Airborne Brigade are capable of airborne operations, in cooperation with the U.S. Air Force's transport aircraft. Finally, Infantry Brigade Combat Teams assigned to the 10th Mountain Division specialized in mountain warfare. Standard Infantry Brigade Combat Teams are assigned to the 25th Infantry Division, which offers additional training in jungle warfare. Armored Brigade Combat Teams comprise mechanized infantry battalions mounted in the M2 Bradley infantry fighting vehicle. Divisions with Armored Brigade Combat Teams include the 1st Infantry Division, 3rd Infantry Division, 4th Infantry Division, 1st Armored Division, and 1st Cavalry Division. Stryker Brigade Combat Teams are centered around Stryker infantry battalions operating out of the Stryker. Divisions with Stryker Brigade Combat Teams include the 2nd Infantry Division, 4th Infantry Division, 11th Airborne Division, 2nd Cavalry Regiment, and 3rd Cavalry Regiment. United States Army Rangers with the 75th Ranger Regiment are an elite special operations infantry force in United States Army Special Operations Command, specializing in air assault and airborne infiltration methods. The three primary missions of the 75th Ranger Regiment are