rank of a unit identity matrix of order 4 is
Identity matrix The identity matrix of a given size is the only idempotent matrix of that size having full rank. That is, it is the only matrix such that (a) when multiplied by itself the result is itself, and (b) all of its rows, and all of its columns, are linearly independent.
List of United States Navy four-star admirals There have been 263 four-star admirals in the history of the U.S. Navy. Of these, 222 achieved that rank while on active duty, 40 were promoted upon retirement in recognition of combat citations, and one was promoted posthumously. Admirals entered the Navy via several paths: 232 were commissioned via the U.S. Naval Academy (USNA), 17 via Naval Reserve Officers Training Corps (NROTC), 8 via Officer Candidate School (OCS), 2 via warrant, 1 via the Naval Aviation Cadet (NAVCAD) Program, 2 via Aviation Officer Candidate School (AOCS) and 1 via the U.S. Merchant Marine.