YO-257

The YO-257 spent decades ferrying fuel for the Navy before Atlantis Submarines sank her off Waikīkī in 1989 to give their passengers something to look at, and she has repaid the investment as Oʻahu's flagship dive. Upright and tidy on the sand, she has swim-through cutouts at deck level, railings dressed in colorful encrusting growth, and a citizenry of green turtles that rest on her plating between feeding runs. Eagle rays cross the sand, whitetips patrol the scuppers, and every so often the 64-passenger submarine hums past like public transit through your dive. Depth keeps bottom times honest; the mooring makes navigation trivial.

The moment you come for: Turtles bedded on the decks; cut-through swim lanes; the occasional passing tourist submarine.

Topography: A 53-meter navy yard oiler upright on flat sand at about 34 m

Current: Longshore current sweeps the sand flat some days; use the mooring line both directions.

Entry: A short charter run off Waikīkī; boats moor over the wreck and the neighboring San Pedro sits within swimming range for a two-wreck profile.

Hazards: Depth for newer divers; current across the open sand; watch overhead for the submarine's scheduled passes.

Conservation: An artificial reef doing its job — take only photographs, and give resting turtles the legally required distance.

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