The order of commissioned officers from lowest seniority to highest is Ensign, Lieutenant Junior Grade, Lieutenant, Lieutenant Commander, Commander, Captain, Rear Admiral (lower half), Rear Admiral (upper half), Vice Admiral, Admiral and Fleet Admiral. It should be noted that Fleet Admiral (O-11) is a rank that can only be granted during wartime. As of January 2015, the last time it was granted was during World War II.
US Navy ranks are divided into three distinct tiers. The highest tier consists of commissioned officers, who hold the ranks of O-1 to O-11, in ascending level of seniority. The next highest tier consists of warrant officers of the ranks W-1 to W-5. Enlisted members make up the lowest ranks.
Warrant officers rank below commissioned officers but above all enlisted members. Their lowest rank is Warrant Officer (W-1). The remaining ranks are called Chief Warrant Officer with a numerical designation to indicate seniority.
Enlisted members comprise the lowest ranks of the Navy. The order of ranks from lowest to highest is Seaman Recruit, Seaman Apprentice, Seaman, Petty Officer Third Class, Petty Officer Second Class, Petty Officer First Class, Chief Petty Officer, Senior Chief Petty Officer, Master Chief Petty Officer and Master Chief Petty Officer of the Navy.