Rio de Janeiro Maru

The Rio de Janeiro Maru was built in 1930 for the OSK line's emigrant route to South America, a motor liner named for her destination port. The navy took her in 1940, used her first as a submarine tender and then as a transport, and Hailstone's bombers found her at Truk in February 1944; she absorbed her damage slowly and went down quietly the next morning, rolling onto her starboard side on a sandy bottom. She is a dive of oversized details. Her port hull, now the wreck's upper surface, is a field of plating within easy reach of the surface; at the stern, her big twin screws stand in the blue like monuments; and in the aft holds sit crates of beer bottles by the thousand, stacked as the stevedores left them. A stern gun still points at nothing. Like every ship of the Hailstone fleet, she carried men who did not get off, and divers treat her accordingly.

How she sank: Bombed on 17 February 1944 during Operation Hailstone; sank in the early hours of the following day.

Condition: Coherent and stable, with the gradual sagging of a large hull lying on its side for eighty years.

Penetration: Full With Training. Hold entries are broad and forgiving by lagoon standards, but the rotated interior still calls for wreck training and a guide who knows the exits. Entering any overhead environment requires specific training — a wreck certification at minimum, technical wreck training for full penetration.

Recommended certification: Advanced Open Water; wreck training for interiors

Current: Mild · Visibility: 15–30 m

Marine life: Hard corals pave the upturned hull, sweetlips and snappers gather at the stern, and turtles are regular visitors along the rail.

Hazards: Silt in the holds, collapsing internal fittings, and glass and cargo that must be left undisturbed.

Chuuk lagoon monument protection; state dive permit/fee applies.

A war grave of the February 1944 raid; conduct inside the hull should honor that.

The famous bottles stay in their crates — removal is illegal.