Norwegian and Swedish ore traffic was the most important sector in Germany's European trade, and securing it became the principal focus of the navy's trade protection efforts throughout the war. After the successful German invasion of Norway, the navy introduced the convoy of merchant shipping along the Norwegian coast late in 1940. Convoys generally were small—three to six ships—and escorted by a few torpedo boats, trawlers, and light craft. British submarines and aircraft were the principal threats. As the war progressed and British air attacks became more effective, the Germans added defensive coastal antiaircraft batteries and antiaircraft escorts. In addition to ever increasing strikes by shore-based Royal Air Force Coastal Command aircraft, the Royal Navy mounted periodic carrier strikes against German coastal shipping in 1942 and 1943, culminating over the next two years with more concentrated assaults using escort carriers that came close to paralyzing this traffic.
When war with the Soviet Union began, the Soviet navy's Northern Fleet submarines initiated attacks on German shipping around northern Norway and were soon joined by British submarines operating from Kola Bay. Joint operations continued until 1944, when the British crews were sent home and the submarines were turned over to the Soviet navy. Substantial numbers of Soviet naval aircraft also joined the attack against German convoys from 1943. This assault against the northern Norwegian convoys cost the Germans some 500,000 tons of shipping, a relatively small amount considering annual traffic was well in excess of 6 million tons.
War with the Soviet Union also brought the threat of attack on the Swedish ore traffic, primarily by Soviet submarines at first. The Germans endeavored to keep shipping within Swedish territorial waters as far as possible, escorting vessels for the final leg of their passage behind the protection of defensive minefields and net barriers. During 1942 and 1943, Soviet submarines succeeded in sinking only about 20 ships for a total of some 40,000 tons of shipping, out of over 1,900 vessels in convoy representing well over 5.6 million tons of shipping. During 1944, the Soviet army's advances and the defeat of Finland meant that aircraft played a greater role in antishipping operations, but German losses remained relatively light. The collapse of German positions on the Baltic coast early in 1945 required the evacuation by sea of more than 2 million troops and others. Despite some spectacular successes (the sinking of the Wilhelm Gustloff and General Steuben with but 1,200 survivors from the more than 9,000 passengers aboard, for example), Soviet attacks were remarkably ineffective; the Germans lost only about 20 ships with a total of some 100,000 tons of shipping.
The Italian navy began convoying traffic carrying supplies to its forces in Libya almost as soon as it entered the war, for British submarines and aircraft immediately began an interdiction campaign. The navy's responsibilities expanded as Italy undertook campaigns in Yugoslavia and Greece in 1941 and increased still further when Germany took on a larger role in the Balkans and North Africa. During 1941, Italy also began convoying shipping along the Libyan coast. Italian convoys generally were small—three to six merchant vessels, with two or three escorting destroyers or torpedo boats. As British surface forces operating from Malta began attacking Libya-bound shipping, the Italian navy had to deploy heavier covering forces, often including cruisers and eventually battleships, to support particularly valuable convoys. In this struggle over shipping, the British possessed two great advantages: radar, which vastly enhanced the night-attack capabilities of its aircraft and surface ships, and signals intelligence, especially ultra, which consistently gave them advance convoy routing information.
Axis fortunes in this campaign fluctuated greatly. From mid-1941, Axis forces in North Africa required approximately 100,000 tons of supplies each month. But in March 1942, for example, only 47,588 tons got through, whereas in April, 150,389, tons arrived. Overall, the Italian navy succeeded in bringing about 80 percent of all convoyed shipping through to its destination.
Despite its direct experience of successful convoy operations by its destroyers in the Mediterranean during World War I, the Imperial Japanese Navy was very slow to introduce convoying of merchant shipping after the Pacific war began. The navy possessed very few suitable escort vessels at the outbreak of war, which reflected the overwhelming emphasis it placed on planning for the decisive fleet action that was the centerpiece of its operational strategy. Japan's response to the burgeoning unrestricted submarine campaign conducted by the United States against its shipping was to increase aggressive surface and air patrols and continue to eschew defensive convoy of its traffic. Not until the later part of 1944, by which date its merchant fleet had been devastated by American submarines, did the navy begin limited convoy, especially of the crucial tankers carrying fuel from the Dutch East Indies, but by then it was too late.
Paul E. Fontenoy
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