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By Peter Cundall - Chief Researcher, Major Projects Foundation
By Peter Cundall
Chief Researcher, Major Projects FoundationThe Major Projects Foundation is researching many wrecks.
This is the story of just one…
Rio de Janeiro Maru was one of two oil-powered ships built in 1926 for Osaka Shosen K. K. (known today as Mitsui OSK) for their Round the World service from Japan to Brazil.
During the 1920’s and 30’s many Japanese people migrated to South America in search of a better life. The Rio de Janeiro and her sister ship Buenos Aires Maru were used extensively in this trade.
In 1940 the ship was requisitioned by the Imperial Japanese Navy (IJN), first as a transport vessel and then as an auxiliary submarine tender before finally becoming a navy transport.


On the 3rd February 1944 the ship sailed to Chuuk (then called Truk) which was at the time a major fleetbase for the IJN.
The ship carried depth charges, coast defence guns, coal, foodstuffs and mail as cargo.
On the 3rd February 1944 the ship sailed to Chuuk (then called Truk) which was at the time a major fleetbase for the IJN.
The ship carried depth charges, coast defence guns, coal, foodstuffs and mail as cargo.

On the 3rd of February 1944 the ship sailed to Chuuk (then called Truk) which was at the time a major fleetbase for the IJN. The ship carried depth charges, coast defence guns, coal, foodstuffs and mail as cargo.
On the 11th of February 1944 Rio de Janeiro arrived at Chuuk to find the base preparing for possible US Air attack with most large warships having already left. The ship anchored on the east side of Uman Island and discharged much of the cargo. On the 17th and 18th of February, an American Naval Taskforce launched a series of large air attacks on the Atoll. Rio de Janeiro was hit on the first day by two 1000 lb bombs and finally sank early on the second day on her starboard side in up to 35 metres of water.
Today the wreck is slowly corroding with significant damage apparent to the ships’ bow and there are regular reports of oil leaking from the vessel.
As such she is a priority for the Major Projects Foundation’s efforts to mitigate the threat of oil pollution and ensure that Chuuk remains a wreck diver’s paradise, as well as preserving the diverse natural eco systems that exist in the area.
Dr Matt Carter, Research Director for the Major Projects Foundation discusses this wreck in-depth in the following video.


Today the wreck is slowly corroding with significant damage apparent to the ships’ bow and there are regular reports of oil leaking from the vessel.
As such she is a priority for the Major Projects Foundation’s efforts to mitigate the threat of oil pollution and ensure that Chuuk remains a wreck diver’s paradise, as well as preserving the diverse natural eco systems that exist in the area.
Dr Matt Carter, Research Director for the Major Projects Foundation discusses this wreck in-depth in the following video.
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Really informative blog post. Thanks Again. Fantastic. Lyda Holt Vivyan