 An admiral is never referred to as "captain".In the seaborne services, especially for submarine and aviation commands, the commanding officer is often referred to informally as "skipper" whether the officer is a captain or below.For the ground and air forces rank, a captain is of pay grade O-3 (the third officer rank), usually serving as the commander of a company-sized unit in the ground forces, as a flight leader or other squadron officer in air units, or serving as an executive officer or staff officer for a larger unit such as a battalion or squadron.