Major

An officer of high rank in the Marines, in particular a field-grade officer ranking above Captain and below "Lieutenant Colonel."

It is equivalent to the Lieutenant Commander on regular Starfleet ships.

A Major's responsibilities include serving as the main staff officer and task force Executive Officer. Their duties also include acting as a senior staff officer at the squadron and wing levels; in flight squadrons, majors are typically assistant directors or flight commanders.

Note: the Starfleet Marines are now defunct.