On Sunday, June 22, 1941, Adolf Hitler attacked the Soviet Union and committed his forces to a war of attrition that could not be won. It was just one of the many faulty strategic decisions that historians would later say doomed the Axis powers. Another was the failure of the Führer and his partners, Benito Mussolini and Emperor Hirohito, to better coordinate their military efforts. Had they done so, the war may have taken a very different course. The secret submarine convoys between Japan and occupied France provide one frightening hint of what might have been achieved.

After Japan attacked Pearl Harbor and Hitler declared war on the United States, the Axis Tripartite Agreement of September 27, 1940, was amended to provide for an exchange of strategic materials and manufactured goods between Germany, Italy and Japan. Initially, surface ships made these voyages, which were dubbed Yanagi (Willow) missions by the Japanese. As the war at sea began to turn against the Axis, however, submarines were seen to be a better means of transport.

As early as March 27, 1942, the German naval high command requested that the Imperial Japanese Navy (IJN) launch offensive operations against Allied convoys in the Indian Ocean to help relieve some of the pressure on the Kriegsmarine. On April 8, the Japanese agreed to dispatch submarines to the east coast of Africa to support the Germans. Shortly afterward, the IJN’s 8th Submarine Squadron, 1st Division, was withdrawn from Kwajalein in the Marshall Islands and sent to Penang, Malaya.

Commander Shinobu Endo’s I-30 was one of the boats assigned to Captain Noboru Ishizaki’s 8th Submarine Squadron. The boat was a big, fast 357-foot Type B-1 submarine. Once it reached its squadron, I-30 was placed in the Ko (A) detachment with I-10, I-16, I-18 and I-20 and their support ships. On April 22, I-30 departed Penang and a week later assisted in the detachment’s successful attack on British shipping in Diego Suarez, which badly damaged the battleship HMS Ramillies and sank a tanker. After the attack, I-30 patrolled east of Madagascar for a while before being ordered on the first Yanagi mission using a submarine. For the highly important voyage, I-30 was placed directly under the command of Vice Adm. Teruhisa Komatsu’s Sixth Fleet.

On August 2, Endo entered the Bay of Biscay. Off Cape Ortegal, Spain, he was met by eight Luftwaffe Junkers Ju-88A attack bombers that provided air cover. Three days later, he was joined by a flotilla of minesweepers and escorted to Lorient — then the largest of the five German U-boat bases on the French coast.

It was a historic moment. I-30 was the first Japanese submarine to arrive in Europe. As befitted such an important occasion, Grand Admiral Erich Raeder, head of the Kriegsmarine; Admiral Karl Dönitz, commander of the U-boat force; and Captain Tadao Yokoi, Japanese naval attaché to Berlin, were on hand to greet Endo and his crew. The Lorient station band played martial music, and an attractive young woman presented Endo with the bouquet of flowers traditionally given to successful U-boat commanders. While U-boat men fted the Japanese sailors, the sub’s cargo of 3,300 pounds of mica and 1,452 pounds of shellac was unloaded along with engineering drawings of the Japanese Type 91 aerial torpedo.

Kriegsmarine submarine experts examined the Japanese boat thoroughly and concluded that its noise levels were unreasonably high by their standards. They believed that an enemy destroyer’s hydrophones could easily pick up I-30’s location. If they did not, then radar-equipped Allied air patrols most likely would. To counter this, the Germans fitted a Metox ‘Biscay Cross passive radar detector to the bridge of the Japanese sub. They also removed its 25mm Type 96 anti-aircraft guns and replaced them with a quick-firing Mauser quadruple 20mm anti-aircraft mount.

Repairs were also made to I-30’s Yokosuka E14Y1 floatplane, which was repainted with false Japanese unit markings. The Germans then shot film footage during the floatplane’s test flights and later released stories that a Japanese naval air corps was now operating from French bases. While all of this was going on, Endo traveled to Berlin where Hitler presented him with the Iron Cross. The visit came to an end on August 22, when I-30 slipped out of the sub pen and began its journey home. Its cargo included a complete Würzburg air defense ground radar with blueprints and examples of German torpedoes, bombs and fire control systems. Perhaps most important of all, the submarine also carried industrial diamonds valued at one million yen and 50 top-secret Enigma coding machines.

A month later, I-30 rounded the Cape of Good Hope and entered the Indian Ocean. Early on the morning of October 8, the sub arrived back at Penang. Rear Admiral Zenshiro Hoshina, chief of the IJN’s logistics section, was on hand and asked Endo for 10 of the Enigmas. Two days later, I-30 slipped its moorings and headed south for Singapore through the Straits of Malacca.

During the night of October 13, I-30 arrived at Singapore but it was not until the following morning that the submarine was able to make its way into the port. The commander of the First Southern Expeditionary Fleet, Vice Adm. Denshichi Okawachi, and staff of the No. 10 Special Base Unit were on hand to greet Endo and his officers. That same day, the sub’s navigator requested and received maps of the areas around Singapore that had been swept of mines. Anxious to get home, Endo departed Singapore for Kure that afternoon. Along the way I-30 hit a mine just three miles east of Keppel Harbor. The explosion mortally wounded the submarine, but Endo and most of his crew were rescued before it sank.

Divers were immediately dispatched to recover I-30’s cargo, but they found that the Würzburg radar had been destroyed in the blast and its drawings rendered useless by saltwater. In addition, the remaining Enigma machines were lost, a fact that was kept from the Germans for four months.

Although I-30’s voyage had ended somewhat ignominiously, much had been learned and officials on both sides were excited by the potential of the Yanagi missions. On March 31, 1943, the Japanese ambassador to Germany, Hiroshi Oshima, reported to Tokyo that Field Marshal Erich von Manstein had suggested that since so many surface blockade-runners were being sunk that large, older U-boats should be converted to carry war materiel between Europe and the Far East. Oshima recommended that the Japanese adopt Manstein’s suggestion as soon as possible. Oshima’s cable was sent in the Japanese diplomatic Purple code, which was intercepted and decoded by the Allies.

On June 1, I-8 departed Kure with I-10 and submarine tender Hie Maru. Commander Shinji Uchino had just been given his orders to proceed to Lorient. I-8 was a Junsen Type J-3 submarine and its cargo included two Type 95 oxygen-propelled torpedoes, drawings of an automatic trim system, Type 95 submarine torpedo tubes and a new naval reconnaissance plane. Accompanying Uchino was Lt. Cmdr. Sadatoshi Norita and a 48-man spare crew. After receiving training by the Germans in the Baltic, Norita was scheduled to take command of U-1224, a Type IXC/40 U-boat. Other passengers included four translators and code clerks, a medical officer and an expert on torpedo-boat engines. Nine days later Uchino arrived at Singapore and loaded an additional cargo of quinine, tin and raw rubber before heading for Penang. Uchino set out alone on his westward journey in late June. On July 21, I-8 entered the Atlantic and was greeted by fierce storms that battered the submarine for 10 days.

On the 24th, the weary Japanese sailors received the first radio signal from the Germans, who warned their comrades about radar-equipped air patrols. With increased enemy patrol activity, five days later Uchino received a second signal from the Germans instructing him to make for Brest instead of Lorient.

Uchino crossed the equator on August 2, and on the 20th the Japanese rendezvoused with Captain Albrecht Achille’s U-161. The next day, I-8 took aboard a Lieutenant Jahn and two petty officer radiomen. The Germans installed a FuMB 1 Metox 600A radar detector on Uchino’s bridge. On August 29, Uchino entered the Bay of Biscay. The Luftwaffe sent Ju-88s to provide air cover. The Japanese sub arrived safely at Brest two days later. After I-8’s arrival, a German news agency announced that now even Japanese submarines are operating in the Atlantic.

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