Majors can also serve as Company Commanding Officers, a major can also serve as a primary staff officer for a regiment, brigade or task force in the areas concerning personnel, logistics, intelligence, and operations.

In the 1830s, the Army selected an oak leaf as the rank insignia for a major, though the rationale for the choice remains unclear.

A regiment consisted of eight companies with three officers (a captain, lieutenant and ensign) and about 60 enlisted men each.

In the late 1800s the US Army changed from the traditional ten-company regiment to one of twelve companies organized into three four-company battalions, each commanded by a major.

A major in the Air Force typically has duties as a senior staff officer at the squadron and wing level.

In flying squadrons majors are generally flight commanders or assistant directors of operations.

A major in the Space Force typically has duties as a senior staff officer at the squadron and delta levels.