6 or 6

In the United States Navy, United States Coast Guard, United States Public Health Service Commissioned Corps (USPHS), and National Oceanic and Atmospheric Administration Commissioned Officer Corps (NOAA Corps), captain is the senior-most commissioned officer rank below that of flag officer (i.e., admirals). The equivalent rank is colonel in the United States Army, Air Force, and Marine Corps.
Reflecting its nautical heritage, the term "captain" is sometimes used as a military title by more junior officers who command a commissioned vessel of the Navy, Coast Guard, or National Oceanic and Atmospheric Administration ship of patrol boat size or greater. Officers below O-6 who command aviation squadrons (typically O-5 commanders) usually use the less formal title "skipper".

View More On Wikipedia.org