Dictionary.net

A grade created by Act of Congress in 1864. It was at the time of creation the highest naval office, but was outranked by that of admiral, created two years later. By the Act of January 24, 1873, Congress provided that when the offices of admiral and vice-admiral became vacant the grades should cease to exist, that of rear-admiral to be then deemed the highest. On the death of Vice-Admiral Rowan in 1890 the grade became extinct. During the colonial period it was usual for the royal governor of a colony to be also appointed vice-admiral, which made him head of the colonial admiralty courts.

n. A naval officer of the second rank—he flies his flag on the fore-top-gallant mast; formerly, the second officer in command.