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Unless otherwise indicated, all material researched, written, and copyrighted by Bill Stone for publication in various venues online and elsewhere. Feel free to point links at these pages, but reproduction of this material, electronic or otherwise, is prohibited without prior permission in writing from Stone & Stone.

Japanese Submarines at Madagascar and the Mozambique Channel


Although between December 1941 and January 1942 Axis negotiations set longitude 70 degrees east as the boundary between German and Japanese naval operations in the Indian Ocean, exceptions were to be allowed as circumstances warranted. On 14 March Admiral Raeder informed Hitler -- not altogether accurately -- that Japan planned to occupy Ceylon and then establish bases on Madagascar. For that latter island the Japanese would require approval from their German allies (for Madagascar lay on the German side of the boundary line) and from Vichy (who controlled and defended the colony). Hitler, seldom interested in naval affairs, was unenthusiastic and did not expect Vichy to permit Japan to establish bases on the island.

Despite Hitler's lack of interest there were others who took more notice of such strategic possibilities.

Churchill telegraphed to Roosevelt: "A Japanese air, submarine, and/or cruiser base at Diego Suarez [on the northern tip of Madagascar, halfway between Cape Town and Colombo] would paralyse our whole convoy route both to the Middle East and to the Far East...."

Field Marshal Smuts cabled Churchill that Madagascar is "...the key to the safety of the Indian Ocean" and feared that the Japanese might use bases on the island in an advance against the African mainland in the same manner that they had recently used bases in Indo-China in their advance against Burma, Malaya, Singapore, British Borneo, and the Netherlands East Indies.

De Gaulle wished to make a Free French landing on Madagascar, but his failure at Dakar meant that his plans found no support.

Meanwhile, on 27 March the German naval staff requested that the IJN launch operations against Allied convoys in the Indian Ocean. On 8 April the Japanese formally agreed to dispatch submarines to the east coast of Africa.

Japanese forces

The 1st Division of the 8th Submarine Flotilla was withdrawn from its base at Kwajalein in the Marshall Islands and arrived at Penang in northwestern Malaya at the end of April 1942.

Commanded by Rear Admiral Ishizaki, the division was made up of fleet submarines I-10, I-16, I-18, I-20, and I-30. Three carried one midget sub apiece and two carried one aircraft apiece; each was armed with a 5.5" gun. Normal cruising range was 14,000 miles.

The submarines were supported by a pair of auxiliary cruisers/supply ships -- Aikoku Maru and Hokoku Maru -- armed with guns and torpedoes.

To Diego Suarez

I-30 was first to depart Penang (20 April), sending her scout plane over Aden's harbor on 7 May and then working southward with further reconnaissance at Djibouti, Mombasa, Dar-es-Salaam, and Zanzibar. The main body took a more southerly course toward Durban where it undertook reconnaissance. As many as 40 Allied cargo ships lay in Durban roadstead, but the undetected Japanese submarines, seeking warships, were not yet ready to show their hand, and no attacks were launched.

Instead, the subs concentrated off Diego Suarez and one of their planes discovered the British battleship Ramillies berthed there on 29 May. It was at the beginning of the month that Allied forces had finally landed on Madagascar and occupied the northern portion of the island, and the facilities of Diego Suarez now serviced Allied vessels. Although the scoutplane was spotted -- and Ramillies left its berth -- the Japanese flight was believed to be by a Vichy airplane from an airfield down-island.

On the night of the 29th I-16, I-18, and I-20 were ordered to launch their midget subs. The craft from I-18 was not successfully launched due to engine trouble, but at least one of the others penetrated the harbor. At 2025 on 30 May Ramillies was hit by a torpedo and, while British corvettes dropped depth charges, at 2120 the tanker British Loyalty took at least one torpedo and sank.

The I-20's midget sub then grounded on a reef while attempting to retire from the harbor. On 2 June her two-man crew was shot and killed by an Allied patrol near Amponkarana Bay and their documents recovered. The wrecked midget was later sighted by British air reconnaissance.

Prior to discovering the true agent of the attack, Allied planes flew a retaliatory raid against the airfield at Tananarive and claimed to have destroyed three Vichy aircraft.

Ramillies emerged from Diego Suarez on 9 June and limped to Durban for repairs.

The Mozambique Channel

Allied vessels rounding the Cape of Good Hope and heading northward along the eastern coast of Africa toward the Middle East passed through the Mozambique channel between Madagascar and the African mainland. By the summer of 1942 this shipping remained almost invariably without escort and without air cover, and it was to prove a happy hunting ground for Ishizaki's boats.

The two supply ships entered the fray by sinking the Elysia 370 miles ENE of Durban on 5 June. On the same date the subs went into action in the Mozambique channel and sank three Allied merchantmen. Two more were accounted for the following day and an additional five vessels went down in the next few days.

By 10 June, the local Allied naval commander ordered convoys and fast unescorted shipping to detour to the east of Madagascar to avoid the Mozambique channel. The only advice he could give to other shipping was to hug the shoreline.

Shortly thereafter the Japanese submarines sailed to rendezvous with their supply ships southeast of Madagascar for refueling and replenishing. By the end of the month they were back in the channel and had resumed operations against Allied shipping: one vessel sunk on each of the last three days of the month, and three on the first day of July 1942.

In mid-July the Japanese force, having damaged a British battleship and accounted for some 25 ships totaling over 120,000 tons, began withdrawing from African shores and returned to Penang in August. Admiral Ishizaki suffered no loss other than his midget sub at Diego Suarez.


While it is perhaps unlikely that Japan would have been granted bases on Vichy Madagascar (and in any event the bases would probably have proved impossible to sustain), it is interesting to speculate on the effect of a permanent Japanese air and naval presence athwart -- with the Mediterranean virtually closed -- the only convoy route from the UK to British forces in the Middle East.

Likewise, how much more damage could Ishizaki have done if, instead of hunting Allied warships, at the end of May he had charged into the unsuspecting Allied shipping anchored off Durban?

In the final analysis, though, damage done to Allied interests in this part of the world was of much more immediate benefit to Germany than Japan, and the IJN -- already beginning to feel pressure in the Pacific -- was not willing to devote its precious resources to going to the assistance of its Axis partner.

Saga of I-30

One submarine of the Japanese division did not return to Penang at this time. I-30 had, in fact, not returned to the Mozambique channel with its sister ships at the end of June. Instead, it was dispatched on a longer journey in a different direction. I-30 continued westward, around the Cape of Good Hope, then north through the Atlantic and sailed to France, reaching Lorient on 2 August-- the first Japanese submarine to make the voyage during World War II. A week later she began her long journey back to the Far East but on 13 October 1942, after arriving safely back at Penang, I-30 hit a British mine while en route to Singapore and was lost with thirteen of her hundred-man crew.


Boyd, Carl and Akihiko Yoshida. THE JAPANESE SUBMARINE FORCE AND WORLD WAR II. Annapolis, MD: Naval Institute Press, 1995.

Rohwer, Jurgen. AXIS SUBMARINE SUCCESSES, 1939-1945. Annapolis: Naval Institute Press, 1983.

Rohwer, Jurgen and H. Hummelchen. CHRONOLOGY OF THE WAR AT SEA, 1939-1945. Annapolis: Naval Institute Press, 1992.

Roskill, S. W. THE WAR AT SEA, volume II: THE PERIOD OF BALANCE. London: HMSO, 1956.

Turner, Gordon-Cumming, and Betzler. WAR IN THE SOUTHERN OCEANS, 1939-45. Cape Town: Oxford University Press, 1961.

Copyright © 1998 by Bill Stone
May not be reproduced in any form without written permission of Stone & Stone



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16:15 on 22 January 2017