Monsun Gruppe


The Gruppe Monsun or Monsoon Group was a force of German U-boats that operated in the Pacific and Indian Oceans during World War II. Although similar naming conventions were used for temporary groupings of submarines in the Atlantic, the longer duration of Indian Ocean patrols caused the name to be permanently associated with the relatively small number of U-boats operating out of Penang. After 1944, the U-boats of the Monsun Gruppe were operationally placed under the authority of the Southeast Asia U-boat Region.
The Indian Ocean was the only place where German and Japanese forces fought in the same theatre. To avoid incidents between Germans and Japanese, attacks on other submarines were strictly forbidden. Altogether 41 U-boats of all types including transports would be sent; a large number of these, however, were lost and only a small fraction returned to Europe.

Indian Ocean trade routes

The Indian Ocean was considered strategically important, containing India, and the shipping routes and strategic raw materials that the British needed for the war effort. In the early years of the war German merchant raiders and pocket battleships had sunk a number of merchant ships in the Indian Ocean; however as the war progressed it became more difficult for them to operate in the area and by 1942 most were either sunk or dispersed. From 1941, U-boats were also considered for deployment to this area but due to the successful periods known as the First and Second Happy Times, it was decided that sending U-boats to the Indian Ocean would be an unnecessary diversion. There were also no foreign bases in which units could operate from and be resupplied, hence they would be operating at the limits of their range. As a result, the Germans concentrated primarily on their U-boat campaign in the North Atlantic.
Japan's entry into the war in 1941 led to the capture of European South-east Asian colonies such as British Malaya and the Dutch East Indies. In May and June 1942, Japanese submarines began operating in the Indian Ocean and had engaged British forces in Madagascar. The British had invaded the Vichy-controlled island in order to prevent it from falling into Japanese hands – however, as Japan was never known to have had plans to place Madagascar within its own sphere of influence, Britain's defense of the island could also have been surmised to have been a plausible defense against any possibility of Madagascar falling under Germany's own ambitions.

Axis strategic raw materials

The German invasion of the Soviet Union in 1941 had ended the use of overland routes which were for the delivery of strategic materials from southeast Asia, and few Axis ships were able to avoid Allied patrols of the North Atlantic. Japan was interested in exchanging military technology with Germany, the Japanese submarine I-30 initiated the submerged transport of strategic materials in mid-1942 by delivering 1500 kg of mica and 660 kg of shellac. Japanese submarines designed for the vast distances of the Pacific were more capable transports than the compact German U-boats which were designed for operations around coastal Europe; but large Italian submarines had proved ineffective for convoy attacks. The Italian Royal Navy converted seven Italian submarines operating from BETASOM into "transport submarines" in order to exchange rare or irreplaceable trade goods with Japan. They were: The Bagnolin, the Barbarigo, the Cappellini, the Finzi, the Giuliani, the Tazzoli and the Torelli.

Joint operations in the Indian Ocean

The idea of stationing U-boats in Malaya and the East Indies for operations in the Indian Ocean was first proposed by the Japanese in December 1942. As no supplies were available at either location, the idea was turned down, although a number of U-boats operated around the Cape of Good Hope at the time. A few days after Cappellini reached the East Indies, U-511 became the first U-boat to complete the voyage. This boat carried the Japanese naval attache Admiral Naokuni Nomura from Berlin to Kure. The boat was given to Japan as RO-500; its German crew returned to Penang to provide replacement personnel for the main submarine base being established at a former British seaplane station on the west coast of the Malayan Peninsula. A second base was established at Kobe; small repair bases were located at Singapore, Jakarta, and Surabaya. As part of the dispersal of U-boat operations following heavy losses in the North Atlantic in early 1943, Wilhelm Dommes was ordered to sail his U-178 from his operating area off South Africa to assume command at Penang.

Early submarine patrols to Penang

With the base established, twelve submarines were assigned to the "Monsun Gruppe" and directed to proceed to Penang, patrolling along allied trade routes for the duration of their voyage. The group name reflected an intent; that the opening of the Indian Ocean U-boat campaign should coincide with the monsoon season. The Italian armistice with the allies became effective as the operation proceeded. The Italian submarine Ammiraglio Cagni surrendered at Durban, South Africa rather than continuing to Penang. The converted Italian cargo submarines were taken over by Nazi Germany's Kriegsmarine and renumbered with UIT prefixes.
A second wave of Monsun Gruppe U-boats was dispatched from Europe to make up for losses in transit.
Submarines attempting to reach Penang from Europe suffered heavy attrition, first from bombers in the Bay of Biscay, then from air patrols in the mid-Atlantic narrows and around the Cape of Good Hope, and finally from allied submarines lurking around Penang with the aid of decrypted arrival and departure information.
Although operations from Penang had originally been envisioned as patrols along the trade routes while transporting strategic materials to Europe, many were turned back after allied patrols sank South Atlantic refueling assets.
Six boats remaining in Japanese territory were taken over by the Imperial Japanese Navy when Germany surrendered in 1945.