The "Iro" was not a "maru", like most wrecks in the Chuuk lagoon, ie it was not a merchant transport converted to military uses. It was an oil tanker built in 1921-22 expressly for the imperial Japanese navy. Funny she was powered by coal, was a steamer, even though she carried oil for the engines of other ships. One of only 9 oilers in the Japanese navy in WWII, a major weakness.
It participated in most major WWII operations, except Pearl Harbor. During the course of the war, it was hit many times but survived.
It was finally hit by a torpedo in her bow near the Philippines which chopped off a whole bite of the hull at the very front edge. In March 1944 it was limping on her way to Chuuk to be repaired when she learned of operation Desecrate, the American attack on Palau, and she was ordered to Palau, the next maritime line of defense for the imperial navy.
There she was again attacked and finally sunk.
It was salvaged in the 1950s, the Japanese recuperated the bodies and valuable metals but... the boat bringing the remains of the Iro's sailors and any valuables back to Japan sink en route!
The Iro now rests upright, stern sank first and is deep under the sand with prop and rudder clearly visible. A most interesting set of dives.