The highest rank normally achieved in the U.S. Navy is admiral. Admiral is a four-star flag officer ranking and is typically only used in times of war. Admiral is considered the equivalent of a general in other branches of the armed forces.
In addition to admiral, the U.S. Navy has a five-star officer position called fleet admiral, but it is a dormant position, as of 2015. It is reactivated by the president in times of war or if an event occurs where a five-star officer is necessary. The last time an individual was appointed to fleet admiral was when William F. Halsey Jr. became fleet admiral in 1945.