Japanese submarine Yu 1

In the final two years of World War II, the Imperial Japanese Army constructed transport submarines — officially the Type 3 submergence transport vehicle and known to the Japanese Army as the Maru Yu — with which to supply its isolated island garrisons in the Pacific Ocean. Only submarines of the Yu I type were completed and saw service. The Yu I type was produced in four subclasses, each produced by a different manufacturer and differing primarily in the design of their conning towers and details of their gun armament. None carried torpedoes or had torpedo tubes. Yu 1 was both the first Maru Yu submarine constructed and the lead unit of the Yu 1 subclass.^[1]

Yu 1 was laid down on 23 June 1943 by the Hitachi Kasado Works (Hitachi Kasado Seisakujo) at Kudamatsu, Japan.^[1] She was launched on either 16^[2][3] or 29^[1] October 1943 (according to different sources) and delivered to the Imperial Japanese Army sometime between 22 and 31 December 1943.^[1]

Yu 1 initially remained in Japanese home waters while the Japanese Army constructed additional submarines of her class and established a training program for their crews.^[4] In May 1944, the Army created its first submarine combat unit (jissen butai), the Manila Underwater Transport Detachment (Manira Sensuiyuso Hakentai), consisting of Yu 1, her sister ships Yu 2 and Yu 3, and a mother ship.^[4] The detachment got underway from Japan on either 28^[4] or 30^[2] May 1944 (according to different sources) bound for Manila on Luzon in the Philippines.^[2][4] The vessels had a difficult voyage which included a number of mechanical breakdowns, but finally arrived at Manila on 18 July 1944.^[4] After their arrival, the three submarines underwent repairs and thorough overhauls.^[4]

On 20 October 1944, United States Army forces landed on Leyte, beginning both the Battle of Leyte and the broader Philippines campaign of 1944–1945.^[4] In November 1944, all three submarines got underway on their first supply run to Leyte.^[4] Yu 2 never arrived,^[4] but Yu 1 and Yu 3 reached Ormoc on Leyte's west coast on 27 November 1944 and discharged a combined 600 bags of white rice, 50 boxes of field rations, and 300 boxes of radio batteries.^[4]

In December 1944, Yu 1 and Yu 3 were sent to San Fernando on the northwest coast of Luzon.^[4] On 2 January 1945, U.S. aircraft surprised Yu 1 on the surface and sank her in Lingayen Gulf just off Port Poro on Luzon's coast.^[2][4]

• Bagnasco, Erminio (1977). Submarines of World War Two. Annapolis, Maryland: Naval Institute Press. ISBN 0-87021-962-6.
• Bailey, Mark L. (1998). "Imperial Japanese Army Transport Submarines: Details of the YU-2 Class Submarine YU-3". Warship International. XXXV (1): 55–63.
• Carpenter, Dorr B. & Polmar, Norman (1986). Submarines of the Imperial Japanese Navy 1904–1945. London: Conway Maritime Press. ISBN 0-85177-396-6.
• Chesneau, Roger, ed. (1980). Conway's All the World's Fighting Ships 1922–1946. London: Conway Maritime Press. ISBN 0-85177-146-7.
• Mühlthaler, Erich (1998). "Re:Imperial Japanese Army Transport Submarines". Warship International. XXXV (4): 329–330. ISSN 0043-0374.
• Rekishi Gunzō, History of Pacific War Extra, Perfect guide, The submarines of the Imperial Japanese Forces, Gakken, Tokyo Japan, 2005, ISBN 4-05-603890-2.
• Rekishi Gunzō, History of Pacific War Vol.45, Truth histories of the Imperial Japanese Naval Vessels, Gakken, Tokyo Japan, 2004, ISBN 4-05-603412-5.
• Ships of the World No.506, Kaijinsha, Tokyo Japan, 1996.
• The Maru Special, Japanese Naval Vessels No.43 Japanese Submarines III, Ushio Shobō, Tokyo Japan, 1980.
• Atsumi Nakashima, Army Submarine Fleet, "The secret project !, The men challenged the deep sea", Shinjinbutsu Ōraisha, Tokyo Japan, 2006, ISBN 4-404-03413-X.
• 50 year history of the Japan Steel Works (first volume and second volume), Japan Steel Works, 1968.