[Y201K]

To help sargun out more, Hopper was an O-7, where naval officer's ranks go from O-1 (ensign) to O-10 (admiral). This rank -- along with O-8 (rear admiral (upper half)) -- was previously called "commodore," and in some other countries still is, as in Commodore Matthew Perry.

e: What was previously commodore was split into the current two rear admiral ranks.

[delinka]

Nit: although the 'pedia says rear admiral outranks commodore, in the U.S. Navy the rank is equivalent to commodore in other navies.

[icegreentea]

Thats because the US Navy has two rear admiral ranks. The lower rear admiral is a 1 star officer and is equivalent to commodores in other navys. The upper rear admiral is a 2 star officer is equivalent to "normal" rear admirals in most other navies.

[navbaker]

To make it even more confusing, there are still commodores in the US Navy, but they are job positions and not ranks.