Laid down June 30, 1941 at the Kure Naval Arsenal at Kure. Launched June 12, 1941. Commissioned September 23, 1942. Assigned to the Yokosuka Naval District with Lt Sakamoto as captain. Next, assigned to SubRon 7 in SubDiv 13.
On December 20, 1942 departed for Rabaul, via Truk Lagoon arriving December 28 and departs on January 6, 1943, but develops engine trouble and returns the next day. Under repair and finally departs on February 3. In transit, accidentally bombed by a 958th Kokutai E13 Jake, but sustains only minor damage. Finally arrives at Rabaul on February 7.
Departs on February 8 for a patrol east of Port Moresby. While tracking a merchant ship, a destroyer approached unseen and forces the sub to crash dive to 140' and drops depth charges, that damage the sub, cause leaks and damages the periscopes. Returns to Rabaul for repairs on February 20.
One April 1, 1943 departs Rabaul to patrol south east of Guadalcanal. After arrival the gyroscope malfunctions and the patrol must be aborted and returns to Rabaul on April 12, 1943.
Repaired, on April 22, 1943 departs Rabaul to patrol southeast of Guadalcanal without results and returns to Rabaul on May 14, 1943.
On November 23, 1943 at 5:00am departed Rabaul on a supply run bound for Buin.
On November 25, 1943 RO-100 was in the northern passage, west of Okane Island and Oema Island, northeast of Buin, two miles west of Omai Island. At 7:10pm (local) when RO-100 was approaching the north channel to Buin, a U. S. Navy (USN) sea mine explodes beneath her port side amidships hull. The force of the explosion throws lookouts on the bridge into the sea and the vessel to rapdily sink. Thirty eight of the crew are lost in the sinking.
Fate of the Crew
Some of the surviving crew were attacked by sharks. Only twelve of the crew survive.
IJN Submarine RO-100: Tabular Record of Movement
Most Dangerous Sea page 102
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November 16, 2018