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History
Japan
Name	Yu 21
Builder	Hitachi Kasado Works, Kudamatsu, Japan
Fate	Surrendered August 1945; Scuttled or scrapped;
General characteristics Yu I type
Type	Transport submarine
Displacement	274 long tons (278 t) surfaced; 346 long tons (352 t) submerged;
Length	41.40 m (135 ft 10 in) overall
Beam	3.90 m (12 ft 10 in)
Draft	3.00 m (9 ft 10 in)
Propulsion	2 × Hesselman engines; 298 kW (400 bhp) surfaced; 56 kW (75 shp) submerged; single shaft;
Speed	10 knots (19 km/h; 12 mph) surfaced; 4 knots (7.4 km/h; 4.6 mph) submerged;
Range	1,500 nmi (2,800 km; 1,700 mi) at 8 knots (15 km/h; 9.2 mph) surfaced; 32 nmi (59 km; 37 mi) at 4 knots (7.4 km/h; 4.6 mph) submerged;
Test depth	100 m (328 ft)
Capacity	24 tons freight or 40 troops
Complement	23
Armament	1 × Type 4 37 mm shipboard gun; 5 × Type 99 light machine guns;

Yu 21 was an Imperial Japanese Army transport submarine of the Yu 1 subclass of the Yu I type. Constructed for use during the latter stages of World War II, she served in the waters of the Japanese archipelago.

Construction

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 21 was a unit of the Yu 1 subclass.^[1]

The Hitachi Kasado Works (Hitachi Kasado Seisakujo) at Kudamatsu, Japan, constructed Yu 21.^[1]^[2] Records of the details of the construction of Yu 21 have not been discovered, but the earlier Yu I-type submarines were laid down and launched during the latter half of 1943 and entered service at the end of 1943 or early in 1944.^[2]^[3]

Service history

Yu 21 spent her operational career in Japanese home waters.^[4] Surviving records of the activities of Imperial Japanese Army submarines are fragmentary,^[3]^[5] and no records have been discovered describing her specific activities in support of any particular operation.^[2]^[4]

World War II ended with the cessation of hostilities on 15 August 1945. Yu 21 surrendered to the Allies later in August 1945.^[2] She subsequently either was scuttled or scrapped.^[4]

References

Footnotes

^ ^a ^b Mühlthaler, p. 329.
^ ^a ^b ^c ^d IJA Subs, ijnsubsite.com Accessed 14 May 2022
^ ^a ^b Mühlthaler, pp. 329–330.
^ ^a ^b ^c Mühlthaler, p. 330.
^ Bailey, pp. 55–57, 63.

Bibliography

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, England: Conway Maritime Press. ISBN 0-85177-396-6.
Chesneau, Roger, ed. (1980). Conway's All the World's Fighting Ships 1922–1946. London, England: 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.