The United States Navy (USN) rank system is made up of eight different ranks, ranging from Ensign (ENS) to Chief Warrant Officer (CWO). Ensign is the lowest rank and is three letters long. Commander (CMDR) is the next rank up and is four letters long. Captain (CAPT) is the third rank and is also four letters long. Admiral (ADM) is the fourth rank and is three letters long. Commander (CDR) is the fifth rank and is three letters long. Chief Petty Officer (CPO) is the sixth rank and is three letters long. Commander (CPT) is the seventh rank and is three letters long. Finally, Chief Warrant Officer (CWO) is the highest rank and is three letters long.