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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 Shortly afterward, the IJN’s 8th Submarine Squadron, 1st Division, was withdrawn from Kwajalein in the Marshall Islands and sent to Penang, Malaya.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.

Following a stay of a little more than a month, the Japanese submariners departed Brest on October 5. Their cargo included machine guns, bombsights, a Daimler-Benz torpedo boat engine, naval chronometers, radars, sonar equipment, anti-aircraft gunsights, electric torpedoes, naval chronometers and penicillin. In addition, Uchino welcomed aboard now Rear Adm. Yokoi, naval attaché to Berlin since September 1940, and Captain Sukeyoshi Hosoya, naval attaché to France since December 1939. The sub also carried three German naval officers, an army officer and four radar and hydrophone technicians.

After crossing the equator, Uchino sent a position report to the Germans, but the signal was intercepted by the Allies. The next day I-8 was attacked by an antisubmarine aircraft, but managed to crash-dive and escape. On November 13, 1943, the submarine passed Cape Town, South Africa. That same day, I-34, which had just begun its own mission to France, was torpedoed by the British submarine Taurus south of Penang and earned the unfortunate distinction of being the first IJN submarine sunk by a British submarine. In view of the danger now posed by Allied subs, Uchino was ordered to head directly for Singapore, where he arrived on December 5.

Uchino anchored near Commander Takakazu Kinashi’s I-29, which had just arrived from Kure and was about to set out on its own mission to France. The two commanders met and Uchino warned his counterpart of the many radar-equipped Allied air patrols he had encountered. He also praised the Metox radar detector that he had received from U-161.

After a short rest at Singapore, I-8 began the last leg of its long journey home and finally arrived safely at Kure on December 21, completing a voyage of 30,000 miles. Uchino proceeded to Tokyo and presented his report to Admiral Osami Nagano, chief of the naval general staff, and navy minister Admiral Shigetaro Shimada.

Meanwhile, Kinashi had set out on his own trip to the Atlantic. The veteran submarine captain had not taken part in any previous Yanagi missions when he met with Uchino, but as I-19‘s skipper he had become Japan’s leading underwater ace, credited with sinking the U.S. Navy carrier Wasp off Guadalcanal on September 15, 1942, and damaging the battleship North Carolina and the destroyer O’Brien, which eventually broke in two and sank. I-29 was Kinashi’s seventh command.

While Kinashi was new to the Yanagi missions, his boat and much of his crew were not. On April 5, 1943, I-29 had left Penang on a secret operation. It carried 11 tons of cargo, including one Type 89 torpedo, two Type 2 aerial torpedoes and two tons of gold bars for the Japanese embassy in Berlin. I-29 also carried drawings and blueprints of a Type A midget submarine and of carrier Akagi, which the Germans wanted to study as they constructed their own carrier Graf Zeppelin. On April 25, about 450 miles southeast of Madagascar, I-29 arrived at a predesignated point where it planned to meet Captain Werner Musenberg and U-180. Musenberg’s boat was the first to make the eastward journey to rendezvous with the Japanese. The German sub had left Kiel on February 9 carrying blueprints for a Type IXC/40 U-boat, a sample of a German hollow charge, a quinine sample for future Japanese shipments, gun barrels and ammunition, three cases of sonar decoys, and documents and mail for the German embassy in Tokyo. The U-boat also carried Subhas Chandra Bose, the head of the anti-British Indian National Army of Liberation and his Muslim aide Major Habib Hassan, a former Oxford student. The two boats met, as scheduled, on April 26.

After the transfer of a German officer and a signalman, the two submarines continued together on a northeasterly course waiting for the seas to calm enough for the two to exchange their cargos. The next day, Bose and his group rode a rubber raft from U-180 to I-29 and two Japanese officers transferred to the U-boat. The 11 tons of cargo was then moved in three inflatable rafts while both submarines had their torpedo hatches open. After the passenger and cargo exchanges were completed, I-29 turned eastward and U-180 turned toward the Cape of Good Hope for the Atlantic and its base at Bordeaux, France.

This experience was helpful to Kinashi when he finally set out for France on December 16. In addition to his crew, he carried rubber, tungsten, tin, zinc, quinine, opium and coffee. He also had 16 IJN officers, specialists and engineers on board. Most had originally been scheduled to depart with the ill-fated I-34. After a week at sea, I-29 was refueled from the small German supply ship Bogota. The entire operation took almost six hours, after which the Japanese sub proceeded on its way. On January 8, 1944, the submarine passed south of Madagascar.

In early February Kinashi received a signal from Germany to rendezvous with a U-boat that would supply him with a newer radar detector. On the 12th, he met Lieutenant Hans-Werner Offermann’s U-518 southwest of the Azores. The Japanese submarine took aboard three technicians who removed the Metox radar detector that had been taken from Uchino’s boat and installed a new FuMB 7 Naxos detector on the bridge.

Kinashi had a chance to try out his new equipment on March 4 while running on the surface off Cape Finisterre. That evening, an RAF patrol plane carrying a 22-million candlepower, 24-inch searchlight suddenly illuminated the water around I-29. Reacting with the speed and efficiency gained from long experience, Kinashi and his crew managed to crash-dive their submarine and escaped unharmed. Five days later, I-29 entered the Bay of Biscay, but Kinashi had arrived ahead of his escort and had to spend the night on the bottom. The next morning I-29 rendezvoused with five Junkers Ju-88C fighters. That afternoon, two German destroyers and two torpedo boats joined him and escorted the Japanese submarine toward Lorient. Kinashi was not safe yet, though.

Allied code-breakers had intercepted transmissions that indicated I-29‘s likely position and schedule. They had dispatched two specially equipped de Havilland Mosquitoes armed with 57mm cannons and four other Mosquitoes from No. 248 Squadron RAF to attack the submarine and its escorts. The British found the ships off Cape Peas, Spain, being circled by eight Ju-88Cs. The Mosquito fighters tried to draw the German aircraft away so that the cannon-armed Mosquitoes could attack the sub and its escorts. The British succeeded in downing one Ju-88, but I-29 was undamaged in the action. Later that day, the submarine and its escorts were attacked by more than 10 Allied aircraft, including Bristol Beaufighters and Consolidated B-24 Liberators. Fortunately for Kinashi and his crew, all the bombs missed.

Finally, on March 11, I-29 arrived safely at Lorient and anchored next to Lt. Cmdr. Max Wintermeyer’s U-190. Later, I-29 was berthed in one of the port’s massive Keroman sub pens. Lorient was the home of two U-boat flotillas, and the large number of veteran submariners around the base ensured that some memorable social events occured. On one occasion, German officers entertained their Japanese counterparts at a dockside bar. The bar’s low ceiling rafters were covered with signatures of U-boat officers. Not to be outdone, I-29‘s chief engineering officer Lieutenant Hiroshi Taguchi, chief navigation officer Lieutenant Hideo Otani and several other officers added their carved signatures to the bar’s rafters.

Later, the Germans hosted the entire crew at Château de Trévarez before sending them by special train to Paris. While his crew enjoyed the City of Light, Kinashi traveled to Berlin to be decorated with the Iron Cross by the Führer. As the Japanese relaxed, their hosts removed four outdated anti-aircraft guns from their submarine and replaced them with heavier 37mm Krupp anti-aircraft guns and one 20mm Mauser. In addition, a HWK 509A-1 rocket motor that was used on the Messerschmitt Me-163 Komet rocket interceptor and a Jumo 004B axial-flow turbojet used on the Messerschmitt Me-262 jet fighter were loaded aboard. I-29 also received drawings of the Isotta-Fraschini torpedo boat engine, a V-1 buzz bomb fuselage, acoustic mines, bauxite ore and mercury-radium amalgam. There is also evidence to suggest that I-29 carried a quantity of U-235 uranium oxide, which after refining could have been used in an atomic bomb. Two officers were entrusted with blueprints of the Me-163 and Me-262 jet fighters and plans for rocket launch accelerators. They also received plans for a glider bomb and radar equipment. Finally, 20 more Enigma coding machines were stuffed aboard. Loaded with vital military plans and hardware, I-29 departed Lorient on April 16.

On June 11, the sub passed I-52 in the South Atlantic. The submarines did not communicate, but Kinashi picked up some German radio traffic addressed to I-52. Eighteen days later, I-29 entered the Indian Ocean and on July 13 rendezvoused with its air escort. The next day the sub passed through the Straits of Malacca and arrived safely at Singapore. At the former Royal Navy base I-29‘s passengers disembarked with their plans and documents and proceeded by air to Japan. Most of the scientific cargo, however, remained aboard.

Anxious as to the exact whereabouts of the Japanese sub, Allied code-breakers were greatly relieved when they intercepted a signal that indicated its arrival in Singapore. Relief quickly turned to alarm when, on the heels of the first intercept, a message from Berlin to Tokyo was received that gave the details of the submarine’s strategic cargo. Aware of the frightening potential of what was being carried in I-29‘s hold, Allied intelligence began working around the clock to devise a way to intercept the submarine before it could reach Japan.

Their prayers were answered on July 20, when Kinashi transmitted his proposed route for the last leg of the trip. The U.S. Navy’s Fleet Radio Unit, Pacific (FRUPAC) intercepted and deciphered the message. FRUPAC alerted Vice Adm. Charles A. Lockwood of I-29‘s planned route, cargo and schedule from Singapore to Japan. The admiral then sent a top-secret signal to Commander W.D. Wilkins with that information. Wilkins commanded a wolf pack that included his own USS Tilefish as well as the submarines Rock and Sawfish. He was told that it was imperative that I-29 be intercepted and its cargo prevented from reaching Japan.

Unaware that his travel plans had been discovered, on the morning of July 22, Kinashi left Singapore. Three days later, he reported sighting a surfaced enemy submarine. The next afternoon, as I-29 was itself running on the surface through the western entrance of the Balintang Channel in the Luzon Strait, a lookout on Commander Alan B. Banister’s Sawfish sighted the sub. Banister fired four torpedoes at I-29. Three of them hit, and the Japanese submarine exploded and sank almost immediately.

Three of the Japanese crew were blown clear of their doomed boat, and one of them managed to swim ashore to a small Philippine island and report on I-29‘s fate. The loss of the aircraft engines slowed the Japanese jet program, but their blueprints, flown to Tokyo, arrived safely. They were used immediately to develop the Nakajima Kikka (orange blossom) based on the Me-262 and the Mitsubishi J8MI Shusui (sword stroke) based on the Me-163.

Hope for additional technological treasures now rested on Commander Kameo Uno’s I-52, which had left Kure on March 10, 1944, while I-29 was making its dash for Brest. I-52 was a Type C-3 attack submarine, much slower than the more nimble B-1. In its hold, Uno’s submarine carried strategic metals including molybdenum, tungsten and 146 bars of gold packed in 49 metal boxes, as well as opium and some caffeine. I-52 also carried 14 passengers including engineers and technicians who were to study German weapon systems.

Upon arrival in Singapore, Uno added tin, rubber and quinine to his cargo. On April 23 he departed Singapore for Lorient via the Sunda Strait and the Indian Ocean. His plan was to sail around the Cape of Good Hope. To avoid Allied spotter planes, he traveled submerged during the day and only surfaced at night to recharge his batteries.

After passing the Cape of Good Hope and entering the South Atlantic, on May 15 Uno sent his first message to Germany. By this time the British and Americans had broken the military codes of both the Germans and Japanese. Allied intelligence intercepted and deciphered Uno’s reports to Tokyo and Berlin, including his daily noon position reports. When I-52 entered the South Atlantic, the code-breakers quickly relayed its position and predicted route to a U.S. navy antisubmarine-warfare (ASW) task force.

On June 6, Rear Adm. Hideo Kojima, Yokoi’s replacement as the Japanese naval attaché in Berlin, informed Tokyo and I-52 that the Allies had landed at Normandy. He advised I-52 that it might have to divert to Norway and instructed Uno to rendezvous with a U-boat on June 22. He then signaled Tokyo what I-52‘s position would be. That radio transmission was intercepted, decoded and passed by special-intelligence Ultra signals to an American ASW group operating near the Azores.

On June 16, I-52 sent a coded transmission that its position was off West Africa. Captain A.B. Vosseller’s small escort carrier USS Bogue, with 14 aircraft, was ordered to hunt down and destroy I-52. After arriving in the area where the Japanese sub was supposed to meet the U-boat, Vosseller began around-the-clock flights of Grumman TBF Avenger torpedo bombers to search for the Axis submarines.

Although the skies were filled with American aircraft, Uno rendezvoused with Kurt Lange’s U-530 about 850 miles west of the Cape Verde Islands as scheduled. The Japanese commander welcomed a Lieutenant Schäfer on board to help navigate the last leg of his journey. Schäfer was accompanied by two petty officers who carried improved Naxos FuMB7 radar with them. During the exchange, the radar detector fell into the sea, but a Japanese seaman jumped in and retrieved it. About two hours after meeting I-52, U-530 submerged and headed for Trinidad, leaving the three German officers aboard the Japanese sub.

The day after his rendezvous with U-530, Uno, believing he could take advantage of a dark moonless night during stormy weather to cloak his location, traveled along the surface in order to reach the safety of a German-held port sooner. At about 11:40 in the evening, an Avenger piloted by Lt. Cmdr. Jesse D. Taylor picked up I-52 on its radar. Taylor dropped flares that illuminated the area around the submarine and then dropped two 354-pound bombs that barely missed its starboard side. Uno crash-dived. Although he had successfully evaded Taylor’s attack, he now had been located.

Taylor and his crew dropped sonobuoys over a square mile of ocean. The buoys transmitted any underwater sounds. Within minutes the Avenger’s crew heard I-52‘s propellers in their headsets. Taylor maneuvered his plane into position and dropped a new top-secret Mark 24 Fido acoustic homing torpedo into the water. The torpedo was designed to home in on the propeller noise that had been picked up by the buoys. After a long wait, Taylor’s crew heard a loud explosion.

On June 24, another Avenger, this one piloted by Lieutenant William D. Gordon, arrived and dropped more sonobuoys. Gordon’s crew picked up the sounds of the damaged submarine’s propellers. At about 1 a.m., Gordon launched another Fido toward the submarine. Gordon and his crew soon heard the submarine breaking up underwater. The next day Janssen, one of Bogue‘s destroyer escorts, found a large oil slick at the site of Gordon’s attack and salvaged more than a ton of raw rubber bales floating amid other debris on the surface.

Back at Lorient, a German ship stood by to escort I-52, and diplomats scheduled to return to Japan waited anxiously for their ride home. With them at the dock were tons of secret documents, drawings and strategic cargo, which included T-5 acoustic torpedoes, a Junkers Jumo 213-A engine used on the long-nosed Focke Wulf Fw-190D fighter, radars, vacuum tubes, ball bearings, bombsights, chemicals, alloy steel, optical glass and 1,000 pounds of uranium oxide. The Germans also intended to equip I-52 with a snorkel.

On August 30, the Kriegsmarine finally declared I-52 presumed sunk in the Bay of Biscay as of July 25. With the Americans closing in on the Home Islands and the final showdown of the war in the Pacific fast approaching, the IJN needed to husband every available resource. After the failure of I-52‘s mission, it no longer tried to send its submarines to Europe.

Although the Yanagi missions are today little more than historical footnotes, they serve as an example of what the Axis powers might have been able to accomplish with greater coordination. The prospect of an exchange of nuclear weapon and jet engine technology was sufficiently alarming to Allied officials that they devoted considerable energy to finding and sinking the Japanese submarines before they could deliver their most important cargoes. It is fortunate that they did.


This article was written by Bob Hackett and originally appeared in the October 2005 issue of World War II magazine. For more great articles subscribe to World War II magazine today!