August 16, 1943 the Japanese submarine RO-35 sailed from Truk for the New Caledonia area for reconnaissance mission, the boat was never seen again. RO-35 was a new boat having been completed in March. Eighteen boats in the RO-35 class, Type K6, were completed, they were 264' long and displaced 1,115 tons. They had four 21" torpedo tubes and carried 10 torpedoes, but RO-35 never fired a one.

It is thought that she may have been sunk on Aug. 25 in a depth charge attack by USS Patterson DD-392, but as the wreck has not been located this conclusion is only speculation. What really happened to the RO-35 and the fifty-five men in her is still unknown.

Seventeen of the eighteen boats in the class were lost during the war, the only survivor, RO-50, was surrendered at Sasebo and later scuttled by the U.S. Navy.