Japanese submarine I-73

The Japanese submarine I-73 was a Kaidai type cruiser submarine of the KD6A sub-class built for the Imperial Japanese Navy (IJN) during the 1930s. One month after participating in the IJN's attack on Pearl Harbor, she was sunk by United States Navy submarine USS Gudgeon.

Empire of Japan
Name: I-73
Launched: 1935
Fate: Sunk by USS Gudgeon, 27 January 1942
General characteristics
Class and type: Kaidai type (KD6A sub-class)
  • 1,814 tonnes (1,785 long tons) surfaced
  • 2,479 tonnes (2,440 long tons) submerged
Length: 104.7 m (343 ft 6 in)
Beam: 8.2 m (26 ft 11 in)
Draft: 4.57 m (15 ft 0 in)
Installed power:
  • 9,000 bhp (6,700 kW) (diesels)
  • 1,800 hp (1,300 kW) (electric motors)
  • 23 knots (43 km/h; 26 mph) surfaced
  • 8 knots (15 km/h; 9.2 mph) submerged
  • 14,000 nmi (26,000 km; 16,000 mi) at 10 knots (19 km/h; 12 mph) surfaced
  • 65 nmi (120 km; 75 mi) at 3 knots (5.6 km/h; 3.5 mph) submerged
Test depth: 75 m (246 ft)
Complement: 70

Design and description

The submarines of the KD6A sub-class were versions of the preceding KD5 sub-class with greater surface speed and diving depth. They displaced 1,814 tonnes (1,785 long tons) surfaced and 2,479 tonnes (2,440 long tons) submerged. The submarines were 104.7 meters (343 ft 6 in) long, had a beam of 8.2 meters (26 ft 11 in) and a draft of 4.57 meters (15 ft 0 in). The boats had a diving depth of 75 m (246 ft)[1]

For surface running, the boats were powered by two 4,500-brake-horsepower (3,356 kW) diesel engines, each driving one propeller shaft. When submerged each propeller was driven by a 900-horsepower (671 kW) electric motor.[2] They could reach 23 knots (43 km/h; 26 mph) on the surface and 8 knots (15 km/h; 9.2 mph) underwater. On the surface, the KD6As had a range of 14,000 nautical miles (26,000 km; 16,000 mi) at 10 knots (19 km/h; 12 mph); submerged, they had a range of 65 nmi (120 km; 75 mi) at 3 knots (5.6 km/h; 3.5 mph).[3]

The boats were armed with six internal 53.3 cm (21.0 in) torpedo tubes, four in the bow and two in the stern. They carried a total of 14 torpedoes. They were also armed with one 100 mm (3.9 in) deck gun for combat on the surface and an 13.2 mm (0.52 in) anti-aircraft machinegun.[3]

Construction and career

I-73 participated in the attack on Pearl Harbor as part of the 3rd Submarine Squadron in the 6th Fleet of the IJN. It was one of the vessels created as part of Japan's 1st Naval Armaments Supplement Programme in 1931. On 27 January 1942,[4] I-73 became the first warship to be sunk by a United States Navy submarine; USS Gudgeon fired three torpedoes at I-73 and destroyed it.[5] Gudgeon claimed that the torpedoes only damaged I-73, but Station HYPO confirmed the loss.[6]


  1. Carpenter & Polmar, p. 96
  2. Chesneau, p. 198
  3. Bagnasco, p. 183
  4. "Gudgeon". Dictionary of American Naval Fighting Ships. Navy Department, Naval History and Heritage Command. Retrieved 31 December 2011.
  5. Bob Hackett; Sander Kingsepp (2001). "HIJMS Submarine I-73: Tabular Record of Movement". Combined Fleet. Retrieved 2012-02-13.
  6. Blair, p.118, names her I-173.


  • Bagnasco, Erminio (1977). Submarines of World War Two. Annapolis, Maryland: Naval Institute Press. ISBN 0-87021-962-6.
  • Blair, Clay, Jr. (1976). Silent Victory. New York: Bantam.
  • 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. Greenwich, UK: Conway Maritime Press. ISBN 0-85177-146-7.
  • Hackett, Bob; Kingsepp, Sander (2001). "IJN Submarine I-73: Tabular Record of Movement". combinedfleet.com. Retrieved 15 August 2015.
  • Rohwer, Jürgen (2005). Chronology of the War at Sea 1939–1945: The Naval History of World War Two (Third Revised ed.). Annapolis, Maryland: Naval Institute Press. ISBN 1-59114-119-2.

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