Military Branches Army Founded in 1775, the Army is the oldest and largest branch of the armed services. The Army is primarily responsible for land-based military operations. Navy The Navy’s mission is to maintain, train, and equip combat-ready Naval forces, and to protect and defend our right to move freely on the oceans. The US Navy is the largest navy in the world. Air Force The Air Force became a separate military service in 1947. It includes aviation forces for both service and combat. Air Force troops are organized, trained, and equipped for offensive and defensive air operations. Marine Corps The Marine Corps specializes in amphibious opera- tions, rapid deployment, and self-sufficiency. An elite fighting force with close ties to the Navy, the Marine Corps is often first on the ground in conflicts. Coast Guard The Coast Guard is primarily concerned with law enforcement, boating safety, sea rescue, and illegal immigration control. During wartime, the Coast Guard can become part of the Navy.