While the Marine Corps falls under the Department of the Navy, its command structure is similar to the Army’s, with teams, squadrons, platoons and battalions, except it follows the “rule of three,” meaning there are usually three of each lower unit within the next larger unit.

The Marine Corps’ principal warfighting organization during large crises is the Marine expeditionary force. The Corps has three MEFs, and each is made up of ground, air and logistics forces. They act as standing Marine air-ground task forces in peacetime and war. MEFs are capable of projecting power on land or at sea and are able to support themselves in combat for up to 60 days.

Another exception to the basic unit structure is Marine aviation, which is broken down into commands made of squadrons, groups and wings. The squadron is the basic tactical and administrative unit. One or more squadrons form a group, and one or more groups form a wing.