Captain (Continental Navy)

In the United States uniformed services, captain is a commissioned-officer rank. In keeping with the traditions of the militaries of most nations, the rank varies between the services, being a senior rank in the naval services and a junior rank in the ground and air forces.

For the naval rank, a captain is a senior officer of pay grade O-6 (the sixth officer rank), typically commanding seagoing vessels, major aviation commands and shore installations. This rank is used by the U.S. Navy, U.S. Coast Guard, U.S. Public Health Service Commissioned Corps, the NOAA Commissioned Corps, and the U.S. Maritime Service.

Of note, and to further complicate the confusion, seaborne services of the United States and many other nations refer to the officer in charge of any seagoing vessel as "captain" regardless of actual rank. For instance, in the civilian merchant marine, the commander of a vessel is also referred to as a captain, and everyone in his boat must abide by his commands. While not an official rank, as in military pay grade, it is an official title and can confuse many individuals who are new to or unfamiliar with naval traditions. One exception to the rule is when an officer of higher rank than captain, such as admiral, is the officer in charge of one or more seagoing vessel(s), such as a carrier battle group. An admiral is never referred to as "captain". An additional item of note is that 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. This rank is used by the U.S. Army, U.S. Air Force, and U.S. Marine Corps.

...
Wikipedia