During March 1942, the Japanese planned a two-part operation by midget submarines in Australian waters and the Indian Ocean. The Indian Ocean operation was to be carried out by the 8th Submarine Group, which was commanded by Commodore Ishizaki Noboru. Ishizaki sortied from Penang, Malaysia, on 30 April with five submarines. Two carried one reconnaissance seaplane each, while the other three each carried one Type A midget submarine. After refueling from the armed merchant cruiser Hokoku Maru on 5 May, the submarines searched for shipping up and down the African coast.
Following their successful invasion of Madagascar, the British fleet had dispersed. Only the battleship Ramillies, three destroyers, and two corvettes remained at Diégo-Suarez. On the night of May 29, one of the Japanese seaplanes flew over Diégo-Suarez and reported the presence of a Queen Elizabeth–class battleship in the harbor. The British spotted the plane but could not intercept it. They believed it was a Vichy French plane scouting for French submarines known to be in the area. The Ramillies was ready to get under way by 5:00 a.m. on 30 May and sailed around the bay to foil an expected attack. During daylight, Fleet Air Arm planes flew antisubmarine patrols over Diégo-Suarez. At dusk, the Ramillies again anchored.
Ishizaki ordered the midget submarines, which were 10 miles out to sea, launched at dusk on 29 May. Only two were launched, and only one entered the harbor. At 8:34 p.m. on 30 May, Lieutenant Saburo Akeida and Petty Officer Masami Takemoto fired a single torpedo that struck the Ramillies, blowing a large hole in the battleship's port bulge and causing her to immediately sink by the bow. An hour later, Saburo and Masami launched their remaining torpedo at the oil tanker British Loyalty, sinking her. The corvettes dropped depth charges throughout the night, damaging the midget, which ran aground. Saburo and Masami got ashore and began walking across northern Madagascar toward a prearranged rendevous. The British believed a French submarine had attacked them. Not until three days later, when a British patrol encountered and killed both Saburo and Masami, did the British realize who had attacked them.
The Ramillies was the largest victim of any Japanese midget submarine attack. Temporarily repaired, she sailed for Durban on 3 June, where complete repairs took nearly a year.
Tim J. Watts
Boyd, Carl, and Akihiko Yoshida. The Japanese Submarine Force and World War II. Annapolis, MD: Naval Institute Press, 1995.; O'Neill, Richard. Suicide Squads: Axis and Allied Special Attack Weapons of World War II: Their Development and Their Missions. London: Salamander Books, 1981.; Roskill, Stephen W. The War at Sea, 1939–1945. Vol. 2, The Period of Balance. London: Her Majesty's Stationery Office, 1957.