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Rio de Janeiro Maru – Passenger liner lying on starboard side. Huge stern gun, many beer bottles, several large gun turrets and gun barrels in holds. Nice engine room.

Depth: 35-110ft/10-33m

Rio de Janeiro MaruThe Rio de Janeiro Maru was a 461ft/140m long ship with a gross tonnage of 9,626 tons. She was driven by twin screws with two 6-cylinder 2-stroke Mitsubishi Sulzer diesel engines. She could carry a complement of 150 crewmembers and 1,140 passengers. The word ‘Maru’ designates a merchant vessel.

When built in 1930, the Rio de Janeiro Maru was constructed as an eight-deck passenger liner for one of the largest Japanese shipping companies, the Osaka Shosen Kabushiki Kaisha (O.S.K. Line). Widely known internationally since its founding in 1884, the company provided passenger and cargo service throughout the world. At the outbreak of World War II, the O.S.K. Line operated a fleet of 20 motor driven passenger ships.

In preparation for the war, the Japanese Navy requisitioned the ship in 1940 and converted her to a submarine depot ship (sub-tender). At war’s outbreak on December 7th 1941, the Rio de Janeiro Maru was posted to Submarine Squadron 5 of the 1st Battle Fleet, Southern Force based in Hiroshima Bay, Japan. The ship was active in the role of a sub-tender in the Southwest Area of operations until September 1943 when she was returned to the Empire and re-converted into a transport ship.

On July 27th 1942 it was reported that she was attacked by a submarine while enroute to Cam Ranh Bay, Vietnam and reportedly on fire and in danger of sinking. The U.S.S. Spearfish reported that the ship had been hit by two of its four torpedoes launched during a nighttime periscope attack. However, the Rio de Janeiro Maru was able to remain underway, and complete repairs in Hong Kong. Between January 13th and February 17th 1944, she was primarily engaged in the transportation of ordinary military supplies, material and personnel. On February 17th while at the Truk Atoll, she was bombed during Operation Hailstone and sunk at approximately midnight on February 18th. The attack by U.S.S. Yorktown SBDs and U.S.S. Bunker Hill SB2Cs scored direct hits with one or two 1,000 lb. bombs at 1200 hours on the first day of the air strike.

She rests 450 yards from the shore on the east side of Uman Island on her starboard side with the superstructure between 40-80ft/12-24m, and the sea bed at 110ft/33m. There are excellent exterior exploration opportunities with a large stern gun, large propellers, kingposts, long companionways and several explosion holes extending outward indicating internal explosions at the bow. Inside the wreck divers can explore the engine room and holds where they can find crates of beer bottles, gun barrels and 15ft/5m machined wheel turrets.

(Excerpts reprinted with permission from World War II Wrecks of the Truk Lagoon by Dan E. Bailey)

Truk Wreck Diving

Truk Stop Hotel and Truk Lagoon Dive Center
P.O. Box 546, Chuuk State,
Federated States of Micronesia 96942 
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