|Laid down:||September 29, 1940|
|Commissioned:||February 27, 1942|
|Fate:||Sunk by USS Sawfish, July 26, 1944|
|Class and type:||Type B1 submarine|
|Length:||108.5 m (356 ft)|
|Beam:||9.3 m (31 ft)|
|Draught:||5.12 m (16.8 ft)|
|Propulsion:||2-shaft diesel (12,400 hp (9,200 kW)) and electric motor (2,000 hp (1,500 kW))|
|Speed:||23 knots (43 km/h) surface, 8 knots (15 km/h) submerged|
|Range:||14,000 nautical miles (26,000 km) at 16 knots (30 km/h)|
|Test depth:||100 m (330 ft)|
|Complement:||101 officers and men|
|Armament:||6 × 533 mm torpedo tubes forward (17 torpedoes) + 1 × 14 cm/40 11th Year Type naval gun|
|Aircraft carried:||one Yokosuka E14Y "Glen"'Type 0' reconnaissance seaplane (零式小型水上偵察機)|
I-29, code-named Matsu (松, Japanese for "pine tree"), was a B1 type submarine of the Imperial Japanese Navy used during World War II on two secret missions with Germany. She was sunk while returning from the second mission.
This was the most numerous class of Japanese submarines – almost 20 were built, of which only one (I-36) survived. These boats were fast, had a long range, and carried a seaplane, launched via a forward catapult.
The keel of I-29 was laid on 29 September 1940 at the Yokosuka Naval Yard, and she was commissioned on 27 February 1942, into the 14th submarine squadron under the command of Lieutenant Commander (later Captain) Izu Juichi (伊豆壽市).
Yanagi missions were enabled under the Axis Powers' Tripartite Pact to provide for an exchange of personnel, strategic materials and manufactured goods between Germany, Italy and Japan. Initially, cargo ships made the exchanges, but when that was no longer possible submarines were used.
Only five other submarines attempted this trans-oceanic voyage during World War II: I-30 (April 1942), I-8 (June 1943), I-34 (October 1943) and the German submarines 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 HMS Taurus. Later, the famous Japanese submarine I-52 would also share their fate. In 1945 the German U-234 had completed part of the voyage to Japan when news of Germany's surrender to the Allies was announced, and the submarine subsequently was intercepted and boarded off Newfoundland; this marked the end of the German-Japanese submarine exchanges.
I-29 participated in missions supporting the attack on Port Moresby in New Guinea (Operation Mo), and also in the futile search for Task Force 16, that launched the Doolittle Raid on Tokyo in April 1942.
In April 1943, I-29 was tasked with a Yanagi mission. She was commanded by Captain Masao Teraoka, submarine flotilla commander – indicating the importance of the trip. She left Penang with a cargo that included two tons of gold. She met Fregattenkapitän Werner Musenberg's Type IXD-1 U-boat, U-180 on 26 April 1943 off the coast of Mozambique.
During this meeting that lasted over 12 hours due to bad weather, the two Axis submarines swapped several important passengers. U-180 transferred Netaji Subhas Chandra Bose, a leader of the Indian Independence Movement who was going from Berlin to Tokyo, and his Adjutant, Abid Hasan. I-29 in turn transferred two Japanese Navy personnel who were to study U-boat building techniques in Germany: Commander (later posthumously promoted to Rear Admiral) Emi Tetsushiro, and Lieutenant Commander (later posthumously promoted to Captain) Tomonaga Hideo (who was later connected with the German submarine U-234). Both submarines returned safely to their bases. I-29 landed her important passengers at Sabang on Weh Island, located to the north of Sumatra on 6 May 1943, instead of the Penang, to avoid detection by British spies. Bose and Hasan's transfer is the only known record of a civilian transfer between two submarines of two different navies in World War II. Also there were exchange of two tonnes of gold ingots as payment from Japan for weapons technology.
On December 17, 1943, I-29 was dispatched on a second Yanagi mission, this time to Lorient, France, under star Japanese submarine Commander Takakazu Kinashi. At Singapore she was loaded with 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.
In spite of Allied Ultra decrypts of her mission, I-29 managed to reach Lorient 11 March 1944. On her way she was refueled twice by German vessels. Also, she had three close brushes with Allied aircraft tracking her signals. Of special note is the attack of six RAF aircraft including two Mosquito F Mk. XVIII fighters equipped with 57 mm cannon from No. 248 Squadron RAF off Cape Peñas, Bay of Biscay, at , and the protection provided to her during the entry into Lorient by the Luftwaffe's only Long Range Maritime Fighter Unit, V Gruppe/Kampfgeschwader 40 using Ju 88s. At least one Ju 88 was shot down by British fighters over Spanish waters. The Kriegsmarine also provide an escort of two destroyers and two torpedo boats.
She left Lorient 16 April 1944 for the long voyage home with a cargo of 18 passengers, torpedo boat engines, Enigma coding machines, radar components, a Walter HWK 509A rocket engine, and Messerschmitt Me 163 & Messerschmitt Me 262 blueprints for the development of the rocket plane Mitsubishi J8M. After an uneventful trip she arrived at Singapore on 14 July 1944, disembarking her passengers, though not the cargo.
On her way back to Kure, Japan, she was attacked at Balintang Channel, Luzon Strait, near the Philippines by Commander W. D. Wilkins' "Wildcats" submarine task force consisting of Tilefish, Rock and Sawfish, using Ultra signal intelligence. During the evening of 26 July 1944, she was spotted by Sawfish which fired four torpedoes at her. Three hit I-29, which sank immediately at . Only one of her crewmen survived.
Among the dead was I-29's Commanding Officer, Commander Takakazu Kinashi, Japan's highest-scoring submarine "ace". Earlier in the war, as skipper of I-19, Kinashi torpedoed and sank the U.S. aircraft carrier Wasp and damaged both the battleship North Carolina and the destroyer O'Brien during the same attack. O'Brien later sank as a result of the torpedo damage and North Carolina was under repair at Pearl Harbor until November 16, 1942, Kinashi was honored by a rare two-rank posthumous promotion to Rear Admiral.