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HIJMS RO-100 (Kaisho / Type KS)

Short-Range Coastal Submarine

None of the RO-100 class coastal submarines of the Imperial Japanese Navy survived to see the end of World War 2.
Authored By: Staff Writer | Edited: 12/1/2017
National Flag Graphic


Year: 1942
Ships-in-Class: 18
Named Ships: RO-100; RO-101; RO-102; RO-103; RO-104; RO-105; RO-106; RO-107; RO-108; RO-109; RO-110; RO-111; RO-112; RO-113; RO-114; RO-115; RO-116; RO-117
Roles: Hunter; Direct-Attack;
Complement: 38
Length: 199.9 ft (60.93 m)
Width: 20 ft (6.10 m)
Height: 11.5 ft (3.51 m)
Displacement (Surface): 782 tons
Propulsion: 2 x surface diesel engines developing 1,100 horsepower (surface) with 2 x electric motors generating 760 horsepower (submerged) driving 2 x shafts.
Speed (Surface): 14 kts (16 mph)
Speed (Submerged): 8 kts (9 mph)
Range: 3,511 nm (4,040 miles; 6,502 km)
Operators: Imperial Japan
Development and production of the RO-100 series (sometimes referred to as "Kaisho" or "small" or simply Type "KS") of Japanese submarines was started in earnest beginning in 1940. The vessels (eighteen in total) were designed as short-ranged coastal submarines, originally charged with protection of the homeland coast but her service extended with the reach of the Empire as required. The RO-100 were produced with several design faults that would eventually do the type in by limiting her capabilities immensely when facing off against Allied firepower - be it from the sea or air. Amazingly, because of glaring design drawbacks, none of the 18 total RO-100 class of submarines would last through to the end of the war, most falling prey to Allied aircraft attacks and not navy vessels.

Categorized as coastal submarines - and designed as such - the RO-100 series was allowed a shallow overall operating depth limited to just 245 feet. Additionally, the type carried only eight total torpedoes of 533mm size firing from four bow-positioned tubes. A 76mm deck cannon was almost always removed. Power was derived from surface diesels generating 1,100bhp and electric motors producing 760 horsepower and powering two shafts. The smallish internal workings made accommodations for up to 38 sailors and officers.

As the Empire expanded, the requirements of the RO-100 class grew, often forcing it to operate in deep waters against armored targets that it was never intended to come up against. The system could, however, hold its own against the basic merchant vessels on the seas but it became David and Goliath scenarios when the RO-100 class was called to take on the heavily armored and armed US destroyers operating in Pacific waters. This became increasingly the norm as the war progresses. As a result, losses for the type were horrendous, with many being sunk from the air and a handful by a single US Navy destroyer (the USS England to be exact). The RO-100-class was also not helped by its noted poor handling capabilities.

The RO-35 (Type K6) appeared alongside the RO-100 through production and was a larger (and more improved) variant of the base RO-100 class. Only one KO-35 survived the war with no fewer than 60 of the type being canceled before production was underway.

The RO-106 was credited with the sinking of the LST-342 landing ship off the coast of New Georgia while the RO-108 was credited with the sinking of the American destroyer USS Henley off of New Guinea, both actions occurring in 1943. Beyond that, the class was responsible for sinking a total of 35,200 tons of Allied cargo. Production of the KO-100 was undertaken at the Kure Navy Yard and the Kawasaki Yard at Kobe.


4 x 21" (553mm) torpedo tubes (bow mounted; 8 total torpedoes)
1 x 76mm deck gun (optional)

Air Wing

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