'Kiefer' was a German rendezvous area in the Bay of Biscay between the Japanese blockade-running submarine I-29 and U-518, within the 'Yanagi' undertaking, for onward escort to Lorient on the north-west coast of German-occupied France by the destroyers Z 23 and ZH 1 and the torpedo boats T 27 and T 29 (11 March 1944).

The 'Yanagi' undertaking made it possible for the Axis powers to exchange of personnel, strategic materials and manufactured goods between Germany, Italy and Japan. Blockade-running cargo ships were initially used to effect the exchanges, but when this practice became impossible as the Allies tightened their blockades of the Axis nations submarines came to be used.

Other than I-29, only five other submarines made this trans-oceanic voyage. These were the Japanese I-30 (April 1942), I-8 (June 1943), I-34 (October 1943) and the German U-511 (August 1943) and U-234 (May 1945). Of these, I-30 was sunk by a mine and I-34 by the British submarine Taurus. In 1945 U-234 had completed part of her passage to Japan when news was received of Germany’s surrender to the Allies, and the boat was then intercepted and boarded off Newfoundland, marking the end of the German/Japanese submarine exchanges.

By the time of its first 'Yanagi' mission, I-29 had already participated in a mission supporting the 'Mo' attack on Port Moresby in New Guinea, and also in the failed search for the US Task Force 16 which had launched the 'Doolittle Raid' on Tokyo in April 1942. I-29's reconnaissance of Sydney harbour on 23 May 1942 resulted in the Japanese midget submarine attack on the harbour.

It was in April 1943 that I-29, a large boat with surfaced and submerged displacements of 2,584 and 3,654 tons respectively, was allocated a 'Yanagi' mission. The boat departed Penang off the west coast of Malaya with a cargo including two tons of gold, and met U-180 on 26 April 1943 off the coast of Mozambique. During this rendezvous, which lasted more than 12 hours as a result of adverse weather, the two Axis boats exchanged several important passengers. U-180 transferred Netaji Subhas Chandra Bose, a leader of the Indian independence movement who was travelling from Berlin to Tokyo, and his adjutant, Abid Hasan. I-29 transferred two Japanese navy personnel who were to study U-boat building techniques in Germany, and the two tons of gold, which were Japanese payment for German weapons technology. Both boats then returned safely to their bases, though I-29 landed its two passengers at Sabang on Weh island, to the north of Sumatra, on 6 May 1943 rather than Penang in order to avoid detection by British agents.

On 17 December 1943, I-29 departed on a second 'Yanagi' mission, this time to Lorient in German-occupied France. At Singapore the boat embarked 80 tons of raw rubber, 80 tons of tungsten, 50 tons of tin, two tons of zinc, and three tons of quinine, opium and coffee.

Despite Allied 'Ultra' decrypts of her mission, I-29 reached Lorient on 11 March 1944. During its passage, the boat was refuelled twice by German vessels, and there were three occasions in which the boat had close brushes with Allied aircraft tracking its signals. Of particular interest were the attack off Cape Peñas, Bay of Biscay, of six RAF aircraft including two de Havilland Mosquito F.Mk XVIII 'Tse-tse' heavy fighters, each equipped with a 57-mm cannon, of No. 248 Squadron, and the escort provided during the boat’s approach to Lorient by Junkers Ju 88 warplanes of the Luftwaffe’s only long-range maritime fighter unit, the V/Kampfgeschwader 40. At least one of the Ju 88 aircraft was shot down by British fighters over Spanish waters. The Kriegsmarine also provide an escort of two destroyers and two torpedo boats, as noted above.

I-29 departed Lorient 16 April 1944 for its passage home with a cargo of 18 passengers, torpedo boat engines, Enigma coding machines, radar components, a Walter HWK 509A rocket engine, and blueprints of the Messerschmitt Me 163 and Me 262 to aid the Japanese development of the Mitsubishi J8M rocket-powered interceptor and Nakajima Kikka turbojet-powered fighter. After an uneventful passage, on 14 July I-29 reached Singapore, where it landed its passengers but not its cargo.

On its passage back to Kure in Japan, I-29 was attacked in the Balintang Channel of Luzon Strait near the Philippine islands group by Commander W. D. Wilkins’s 'Wildcats' submarine task force (Tilefish, Rock and Sawfish) on the basis of 'Ultra' intelligence. During the evening of 26 July, I-29 was sighted by Sawfish, which fired four torpedoes at the Japanese boat: three struck the boat, which sank immediately leaving only one member of its crew to survive. Among the dead was I-29's commanding officer, Commander Takakazu Kinashi, Japan’s highest-scoring submarine 'ace'. Earlier in the war, while commanding I-19, Kinashi had torpedoed and sunk the US aircraft carrier Wasp and damaged both the battleship North Carolina and destroyer O’Brien during the same attack. O’Brien later sank as a result of the damage she had sustained, and North Carolina was under repair at Pearl Harbor until 16 November 1942.