Kaichū type submarine

The Kaichū type submarine (海中型潜水艦, Kaichū-gata sensuikan) submarines were double-hulled medium-sized submarines of the Imperial Japanese Navy during World War II. They were derived from the Kaigun-shiki Chū-gata Sensuikan (海軍式中型潜水艦, Navy Medium Type submarine).

Class overview
Name: Kaichū type submarines
Builders:
Operators: Imperial Japanese Navy
Subclasses:
  • Kaichū I (Ro-11 class)
  • Kaichū II (Ro-13 class)
  • Kaichū III (Ro-16 class)
  • Kaichū IV (Ro-26 class)
  • Toku-Chū/Kaichū V (Ro-29 class)
  • Kaichū VI (Ro-33 class)
  • Sen-Chū/Kaichū VII (Ro-35 class)
Built: 1917-1944
In commission: 1919-1945

Several variants existed. From 1934 to 1944, the K6 type (Ro-33 Class) and the K7 type (Senchū, Ro-35 Class) were built. They were equipped with a 76.2 mm (3.00 in) L/40 gun and four 53 cm torpedo tubes for ten type 95 Long Lance torpedoes.

Most of these submarines were destroyed in combat, suffering from Allied anti-submarine warfare measures, and only Ro-50 survived the war.

Class variants

The Kaichū type submarines were divided into seven classes:

  • Kaichū I (海中1型（呂一一型）, Kaichū-ichi-gata, Ro-11-class)
  • Kaichū II (海中2型（呂一三型）, Kaichū-ni-gata, Ro-13-class)
  • Kaichū III (海中3型（呂一六型）, Kaichū-san-gata, Ro-16-class)
  • Kaichū IV (海中4型（呂二六型）, Kaichū-yon-gata, Ro-26-class)
  • Toku-Chū/Kaichū V (特中型/海中5型（呂二九型）, Toku-Chū-gata/Kaichū-go-gata, Ro-29-class)
  • Kaichū VI (海中6型（呂三三型）, Kaichū-roku-gata, Ro-33-class)
  • Sen-Chū/Kaichū VII (潜中型/海中7型（呂三五型）, Sen-Chū-gata/Kaichū-nana-gata, Ro-35-class)

Kaichū I (Ro-11 class)
Ro-11 in 1919

Project number S7. In 1910s, the Imperial Japanese Navy (IJN) bought a license of Schneider-Laubeuf design submarine. The IJN used the design as model and built the S Type (Schneider Type) submarine, the Ha-9 and Ha-10. The Kaichū I is the submarine which jumboized the S Type submarines.

  • Boats in class
Boat Builder Laid down Launched Completed Fate
Submarine No. 19
Ro-11[1]		 Kure Naval Arsenal 25-04-1917 25-10-1917 31-07-1919 as Submarine No. 19 Renamed Ro-11 01-11-1924. Decommissioned 01-04-1932.
Submarine No. 20
Ro-12		 Kure Naval Arsenal 25-04-1917 01-12-1917 18-09-1919 as Submarine No. 20 Renamed Ro-12 01-11-1924. Decommissioned 01-04-1932.

Kaichū II (Ro-13 class)
Ro-15 in 1920s

Project number S18. The Kaichū II had an increased range compared with the Kaichū I, and the turning torpedo tubes were removed.

  • Boats in class
Boat Builder Laid down Launched Completed Fate
Submarine No. 23
Ro-13		 Kure Naval Arsenal 14-09-1918 26-08-1919 30-09-1920 as Submarine No. 23 Renamed Ro-13 01-11-1924. Decommissioned 01-04-1932.
Submarine No. 22
Ro-14		 Kure Naval Arsenal 14-09-1918 31-03-1919 17-02-1921 as Submarine No. 22 Renamed Ro-14 01-11-1924. Decommissioned 01-09-1933.
Submarine No. 24
Ro-15		 Kure Naval Arsenal 12-06-1920 14-10-1920 30-06-1921 as Submarine No. 24 Renamed Ro-15 01-11-1924. Decommissioned 01-09-1933.

Kaichū III (Ro-16 class)
Ro-16 in 1920s

Project number S18. Their project number was the same as in the Kaichū II type submarine, however their performance was improved.

  • Boats in class
Boat Builder Laid down Launched Completed Fate
Submarine No. 37
Ro-16		 Kure Naval Arsenal 18-11-1920 22-04-1921 29-04-1922 as Submarine No. 37 Renamed Ro-16 01-11-1924. Decommissioned 01-09-1933.
Submarine No. 34
Ro-17		 Kure Naval Arsenal 24-09-1920 24-02-1921 20-10-1921 as Submarine No. 34 Renamed Ro-17 01-11-1924. Decommissioned 01-04-1936.
Submarine No. 35
Ro-18		 Kure Naval Arsenal 20-10-1920 25-03-1921 15-12-1921 as Submarine No. 35 Renamed Ro-18 01-11-1924. Decommissioned 01-04-1936.
Submarine No. 36
Ro-19		 Kure Naval Arsenal 09-09-1920 28-12-1920 15-03-1922 as Submarine No. 36 Renamed Ro-19 01-11-1924. Decommissioned 01-04-1936.
Submarine No. 38
Ro-20		 Yokosuka Naval Arsenal 28-07-1919 26-10-1920 01-02-1922 as Submarine No. 38 Renamed Ro-20 01-11-1924. Decommissioned 01-04-1934.
Submarine No. 39
Ro-21		 Yokosuka Naval Arsenal 28-07-1919 26-10-1920 01-02-1922 as Submarine No. 39 Renamed Ro-21 01-11-1924. Decommissioned 01-04-1934.
Submarine No. 40
Ro-22		 Yokosuka Naval Arsenal 22-01-1921 15-10-1921 10-10-1922 as Submarine No. 40 Renamed Ro-22 01-11-1924. Decommissioned 01-04-1934.
Submarine No. 41
Ro-23		 Yokosuka Naval Arsenal 22-01-1921 15-10-1921 28-04-1923 as Submarine No. 41 Renamed Ro-23 01-11-1924. Decommissioned 01-04-1935.
Submarine No. 42
Ro-24		 Sasebo Naval Arsenal 21-04-1919 08-12-1919 30-11-1920 as Submarine No. 42 Renamed Ro-24 01-11-1924. Decommissioned 01-04-1935.
Submarine No. 43
Ro-25		 Sasebo Naval Arsenal 19-02-1920 17-07-1920 25-10-1921 as Submarine No. 43 Renamed Ro-25 01-11-1924. Decommissioned 01-04-1936.

Kaichū IV (Ro-26 class)
Ro-26 in 1923

Project number S18A. Improved model from the Kaichū III type.

  • Boats in class
Boat Builder Laid down Launched Completed Fate
Submarine No. 45
Ro-26		 Sasebo Naval Arsenal 10-03-1921 18-10-1921 25-01-1923 as Submarine No. 45 Renamed Ro-26 01-11-1924. Decommissioned 01-04-1940. Scrapped 1948. Her anchor is displaying at Yokosuka Naval Base.
Submarine No. 58
Ro-27		 Yokosuka Naval Arsenal 16-07-1921 22-07-1922 31-07-1924 as Submarine No. 58 Renamed Ro-27 01-11-1924. Decommissioned 01-04-1936. Scrapped 1948.
Submarine No. 62
Ro-28		 Sasebo Naval Arsenal 10-11-1921 13-04-1922 30-11-1923 as Submarine No. 62 Renamed Ro-28 01-11-1924. Decommissioned 01-04-1940. Scrapped 1948.

Kaichū V (Toku-Chū, Ro-29 class)
Ro-31 in 1935

Project number S18B. They were built for economic-warfare role. The IJN official designation of these boats was Special Purpose-Medium Type submarine (特中型潜水艦, Toku-Chū-gata sensuikan).

  • Boats in class
Boat Builder Laid down Launched Completed Fate
Submarine No. 68
Ro-29		 Kawasaki-Kōbe Shipyard 02-06-1921 05-12-1922 15-09-1923 as Submarine No. 68 Renamed Ro-29 01-11-1924. Decommissioned 01-04-1936.
Submarine No. 69
Ro-30		 Kawasaki-Kōbe Shipyard 27-06-1921 18-01-1923 29-04-1924 as Submarine No. 69 Renamed Ro-30 01-11-1924. Decommissioned 01-04-1942. Scrapped 1945.
Submarine No. 70 Kawasaki-Kōbe Shipyard 25-09-1921 15-02-1923 as Submarine No. 70 Lost in an accident off Awaji Island 21-08-1923. Salvaged and scrapped October 1923. Her materials were used for Ro-31.
Ro-31 Kawasaki-Kōbe Shipyard 20-12-1924 25-09-1926 10-05-1927 Decommissioned 25-05-1945. Scuttled off Sasebo 05-04-1946.
Submarine No. 71
Ro-32		 Kawasaki-Kōbe Shipyard 24-10-1921 19-03-1923 21-05-1924 as Submarine No. 71 Renamed Ro-32 01-11-1924. Decommissioned 01-04-1942. Scrapped 1945.

Kaichū VI (Ro-33 class)
Ro-33 in 1939

Project number S30. They were planned as a prototype for a mass production submarines in the wartime under the Maru 1 Programme.

  • Boats in class
Boat Builder Laid down Launched Completed Results Fate
Ro-33 Kure Naval Arsenal 08-08-1933 10-10-1934 07-10-1935 Sank Australian merchant ship MV Mamutu 07-08-1942 Sunk by HMAS Arunta and RAF patrol aircraft off Port Moresby 29-08-1942.
Ro-34 Mitsubishi-Kōbe Shipyard 25-04-1934 12-12-1935 31-05-1937 Sunk by USS O'Bannon and USS Strong near Russell Islands 06-04-1943.

Kaichū VII (Sen-Chū, Ro-35 class)
Ro-50 in 1944

Project number S44. The final design in the Kaichū series. They were equipped with a Freon air-conditioner, because the IJN took into consideration that they were to be active on the equator area too. The official IJN designation of these boats was Medium Type submarine (中型潜水艦, Chū-gata sensuikan), also called for short, Medium Type (中型, Chū-gata) or Submarine-Medium Type (潜中型, Sen-Chū-gata).
The IJN planned to build these boats under the following Naval Armaments Supplement Programmes:

However some of the boats were cancelled and their naval budgets, materials and staffs were transferred to the I-201 class submarines.

  • Boats in class
Boat No. Boat Builder Laid down Launched Completed Results Fate
201 Ro-35 Mitsubishi-Kōbe Shipyard 09-10-1941 09-06-1942 25-03-1943 Sunk by USS Patterson near of Espiritu Santo 25-08-1943.
202 Ro-36 Mitsubishi-Kōbe Shipyard 07-03-1942 14-10-1942 27-05-1943 Sunk by USS Melvin north of Saipan 13-06-1944.
203 Ro-37 Sasebo Naval Arsenal 09-10-1941 30-06-1942 30-06-1943 Damaged USS Cache 22-01-1944 Sunk by USS Buchanan near of Santa Cruz Islands 11°47′S 164°17′E 22-01-1944.
204 Ro-38 Mitsubishi-Kōbe Shipyard 20-06-1942 24-12-1942 24-07-1943 Disappeared after 19-11-1943.
205 Ro-39 Mitsubishi-Kōbe Shipyard 08-08-1942 06-03-1943 12-09-1943 Sunk by USS Charrette and USS Fair east of Wotje Atoll 06°48′N 168°08′E 03-02-1944.
206 Ro-40 Mitsubishi-Kōbe Shipyard 08-08-1942 06-03-1943 28-09-1943 Sunk by USS Phelps north of Marshall Islands 09°50′N 166°35′E 16-02-1944.
207 Ro-41 Mitsubishi-Kōbe Shipyard 06-10-1942 05-05-1943 26-11-1943 Sank USS Shelton 03-10-1944 Sunk by USS Haggard south of Okinawa 22°57′N 132°19′E 23-03-1945.
208 Ro-42 Sasebo Naval Arsenal 27-04-1942 25-10-1942 31-08-1943 Sunk by USS Bangust northeast of Marshall Islands 10°05′N 168°22′E 10-06-1945.
209 Ro-43 Mitsubishi-Kōbe Shipyard 06-10-1942 05-06-1943 16-12-1943 Damaged USS Renshaw 21-02-1945 Sunk by aircraft from USS Anzio off Iwo Jima 25°07′N 140°19′E 27-02-1945.
385 Ro-44 Mitsui-Tamano Shipyard 14-02-1942 11-11-1942 13-09-1943 Sunk by USS Burden R. Hastings near of Enewetak 11°13′N 164°15′E 16-06-1944.
386 Ro-45 Mitsubishi-Kōbe Shipyard 20-10-1942 21-07-1943 11-01-1944 Sunk by USS Macdonough, USS Stephen Potter and aircraft from USS Monterey south of Truk 06°13′N 151°19′E 01-05-1944.
387 Ro-46 Mitsui-Tamano Shipyard 13-06-1942 23-04-1943 19-02-1944 Damaged USS Cavalier 29-01-1945 Sunk by aircraft from USS Tulagi near of Oki Daitō 24°15′N 131°16′E 29-04-1945.
388 Ro-47 Mitsubishi-Kōbe Shipyard 28-12-1942 20-08-1943 31-01-1944 Sunk by USS McCoy Reynolds northeast of Palau 09°19′N 136°44′E 26-09-1944.
389 Ro-48 Mitsubishi-Kōbe Shipyard 17-03-1943 15-10-1943 31-03-1944 (1) Sunk by USS William C. Miller northwest of Saipan 14-07-1944.
(2) Sunk by USS Wyman northwest of Saipan 18-07-1944.
390 Ro-49 Mitsui-Tamano Shipyard 16-11-1942 03-08-1943 19-05-1944 Sunk by USS Hudson.
391 Ro-50 Mitsui-Tamano Shipyard 18-02-1943 27-11-1943 31-07-1944 Sank USS LST-577 11-02-1945 Decommissioned 30-11-1945. Sunk as target off Gotō Islands 01-04-1946.
392 - 395 Cancelled in 1943.
396 Ro-55 Mitsui-Tamano Shipyard 05-08-1943 23-04-1944 30-09-1944 Sunk by USS Thomason west of Luzon 15°27′N 119°25′E 07-02-1945.
640 - 644 Cancelled in 1943.
645 Ro-56
(ex-Ro-75)		 Mitsui-Tamano Shipyard 02-12-1943 as Ro-75 05-07-1944 15-11-1944 Sunk by USS Mertz and USS Monssen near of Oki Daitō 26°09′N 130°21′E 09-04-1945.
646 - 654 Cancelled in 1943.
5181 - 5223 Cancelled in 1943.

Characteristics
Type Kaichū I (Ro-11) Kaichū II (Ro-13) Kaichū III (Ro-16) Kaichū IV (Ro-26)
Displacement Surfaced 720 long tons (732 t) 740 long tons (752 t) 740 long tons (752 t) 750 long tons (762 t)
Submerged 1,000 long tons (1,016 t) 1,003.1 long tons (1,019 t) 997 long tons (1,013 t) 1,080 long tons (1,097 t)
Length (overall) 69.19 m (227 ft 0 in) 70.10 m (230 ft 0 in) 70.10 m (230 ft 0 in) 74.22 m (243 ft 6 in)
Beam 6.35 m (20 ft 10 in) 6.10 m (20 ft 0 in) 6.12 m (20 ft 1 in) 6.12 m (20 ft 1 in)
Draft 3.43 m (11 ft 3 in) 3.68 m (12 ft 1 in) 3.70 m (12 ft 2 in) 3.73 m (12 ft 3 in)
Power plant and shaft 2 × Sulzer Mk.2 diesels
2 shafts		 2 × Sulzer Mk.2 diesels
2 shafts		 2 × Sulzer Mk.2 diesels
2 shafts		 2 × Sulzer Mk.2 diesels
2 shafts
Power Surfaced 2,900 bhp 2,900 bhp 2,900 bhp 2,900 bhp
Submerged 1,200 shp 1,200 shp 1,200 shp 1,200 shp
Speed Surfaced 18.2 knots (33.7 km/h) 16.5 knots (30.6 km/h) 16.5 knots (30.6 km/h) 16.0 knots (29.6 km/h)
Submerged 9.1 knots (16.9 km/h) 8.5 knots (15.7 km/h) 8.5 knots (15.7 km/h) 8.5 knots (15.7 km/h)
Range Surfaced 4,000 nmi (7,400 km) at 10 knots (19 km/h) 6,000 nmi (11,000 km) at 10 knots (19 km/h) 6,000 nmi (11,000 km) at 10 knots (19 km/h) 6,000 nmi (11,000 km) at 10 knots (19 km/h)
Submerged 85 nmi (157 km) at 4 knots (7.4 km/h) 85 nmi (157 km) at 4 knots (7.4 km/h) 85 nmi (157 km) at 4 knots (7.4 km/h) 85 nmi (157 km) at 4 knots (7.4 km/h)
Test depth 30 m (98 ft) 30 m (98 ft) 45.7 m (150 ft) 45.7 m (150 ft)
Fuel 58.4 tons 75 tons 75 tons 75 tons
Complement 43 43 46 46
Armament (initial) • 6 × 450 mm (18 in) TTs
(4 × front, 2 × turret)
• 10 × Type 44 torpedoes
• 1 × 76.2 mm (3.00 in) L/23.5 5th Year Type AA gun		 • 6 × 450 mm (18 in) TTs
(4 × front, 2 × upper deck)
• 10 × Type 44 torpedoes
• 1 × 76.2 mm (3.00 in) L/23.5 5th Year Type AA gun		 • 6 × 450 mm (18 in) TTs
(4 × front, 2 × upper deck)
• 10 × Type 44 torpedoes
• 1 × 76.2 mm (3.00 in) L/23.5 5th Year Type AA gun		 • 4 × 533 mm (21 in) TTs
(4 × front)
• 8 × 6th Year Type torpedoes
• 1 × 76.2 mm (3.00 in) L/23.5 5th Year Type AA gun
Type Kaichū V (Ro-29) Kaichū VI (Ro-33) Kaichū VII (Ro-35)
Displacement Surfaced 852 long tons (866 t) 700 long tons (711 t) 960 long tons (975 t)
Submerged 1,030 long tons (1,047 t) 1,200 long tons (1,219 t) 1,447 long tons (1,470 t)
Length (overall) 74.22 m (243 ft 6 in) 73.00 m (239 ft 6 in) 80.50 m (264 ft 1 in)
Beam 6.12 m (20 ft 1 in) 6.70 m (22 ft 0 in) 7.05 m (23 ft 2 in)
Draft 3.73 m (12 ft 3 in) 3.25 m (10 ft 8 in) 4.07 m (13 ft 4 in)
Power plant and shaft 2 × Sulzer Mk.1 diesels
2 shafts		 2 × Kampon Mk.21 Model 8 diesels
2 shafts		 2 × Kampon Mk.22 Model 10 diesels
2 shafts
Power Surfaced 1,200 bhp 3,000 bhp 4,200 bhp
Submerged 1,200 shp 1,200 shp 1,200 shp
Speed Surfaced 13.0 knots (24.1 km/h) 19.0 knots (35.2 km/h) 19.8 knots (36.7 km/h)
Submerged 8.5 knots (15.7 km/h) 8.2 knots (15.2 km/h) 8.0 knots (14.8 km/h)
Range Surfaced 6,000 nmi (11,000 km) at 10 knots (19 km/h) 8,000 nmi (15,000 km) at 12 knots (22 km/h) 5,000 nmi (9,300 km) at 16 knots (30 km/h)
Submerged 85 nmi (157 km) at 4 knots (7.4 km/h) 90 nmi (170 km) at 3.5 knots (6.5 km/h) 45 nmi (83 km) at 5 knots (9.3 km/h)
Test depth 45.7 m (150 ft) 75 m (246 ft) 80 m (260 ft)
Fuel 143 tons 109 tons 218 tons
Complement 44 61 61
Armament (initial) • 4 × 533 mm (21 in) TTs
(4 × front)
• 8 × 6th Year Type torpedoes
• 1 × 120 mm (4.7 in) L/45 11th Year Type Naval gun
• 1 × 6.5 mm machine gun		 • 4 × 533 mm (21 in) TTs
(4 × front)
• 8 × Type 89 torpedoes
• 1 × 76.2 mm (3.00 in) L/40 11th Year Type AA gun
• 1 × 13.2 mm (0.52 in) Type 93 AA gun		 • 4 × 533 mm (21 in) TTs
(4 × front)
• 10 × Type 95 torpedoes
• 1 × 76.2 mm (3.00 in) L/40 11th Year Type AA gun
• 2 × Type 96 25mm AA guns

Bibliography
  • "Rekishi Gunzō"., History of Pacific War Vol.17 I-Gō Submarines, Gakken (Japan), January 1998, ISBN 4-05-601767-0
  • Rekishi Gunzō, History of Pacific War Extra, "Perfect guide, The submarines of the Imperial Japanese Forces", Gakken (Japan), March 2005, ISBN 4-05-603890-2
  • The Maru Special, Japanese Naval Vessels No.43 Japanese Submarines III, Ushio Shobō (Japan), September 1980, Book code 68343-44
  • The Maru Special, Japanese Naval Vessels No.132 Japanese Submarines I "Revised edition", Ushio Shobō (Japan), February 1988, Book code 68344-36
  • The Maru Special, Japanese Naval Vessels No.133 Japanese Submarines II "Revised edition", Ushio Shobō (Japan), March 1988, Book code 68344-37
  • The Maru Special, Japanese Naval Vessels No.135 Japanese Submarines IV, Ushio Shobō (Japan), May 1988, Book code 68344-39


References
  1. 呂号第11潜水艦 (Ro-Gō Dai-11 Sensuikan). The same shall apply hereinafter.
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