USNS Vandenberg

The Vandenberg tracked missiles and spacecraft through the Cold War, her giant parabolic radar dishes following launches downrange from Cape Canaveral. Scuttled south of Key West in 2009 as one of the largest artificial reefs ever created, she sits upright with those dishes still mounted - the most surreal photographic subject in the Keys, a satellite ship parked on the seabed. Structure starts around 14-20 m and the tour deepens from there, past kingposts, cranes, and swim-through passages prepped for trained divers. Barracuda and jacks own the superstructure, goliath groupers boom in the interior, and lionfish hunters work her constantly. Two dives minimum; she rewards ten.

The moment you come for: Radar dishes on a sunken tracking ship, huge intact structure, Key West's signature dive

Topography: 159 m missile-tracking ship upright on sand at about 43 m

Current: Seven miles off Key West, exposed to current; multiple moorings let boats work the conditions.

Hazards: Depth and current; genuine overhead spaces beyond the prepared swim-throughs.

Conservation: FKNMS artificial reef; moorings mandatory, removal of anything prohibited.

Nitrox: Worth it here — profiles sit in the range where enriched air meaningfully extends no-stop time (with the training to use it).