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HIJMS RO-100 (Kaisho / Type KS)

Short-Range Coastal Submarine

Imperial Japan | 1942

"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 | Last Edited: 12/01/2017 | Content ©www.MilitaryFactory.com | The following text is exclusive to this site; No A.I. was used in the generation of this content.
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.

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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.

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Power & Performance
Those special qualities that separate one sea-going vessel design from another. Performance specifications presented assume optimal operating conditions for HIJMS RO-100 (Kaisho / Type KS).
2 x surface diesel engines developing 1,100 horsepower (surface) with 2 x electric motors generating 760 horsepower (submerged) driving 2 x shafts.
14.0 kts
16.1 mph
Surface Speed
8.0 kts
9.2 mph
Submerged Speed
3,511 nm
4,040 miles | 6,502 km
The bow-to-stern, port-to-starboard physical qualities of HIJMS RO-100 (Kaisho / Type KS).
199.9 ft
60.93 meters
O/A Length
20.0 ft
6.10 meters
11.5 ft
3.51 meters
Available supported armament and special-mission equipment featured in the design of HIJMS RO-100 (Kaisho / Type KS).
4 x 21" (553mm) torpedo tubes (bow mounted; 8 total torpedoes)
1 x 76mm deck gun (optional)
Ships-in-Class (18)
Notable series variants as part of the HIJMS RO-100 (Kaisho / Type KS) family line as relating to the RO-100 class group.
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
Global operator(s) of the HIJMS RO-100 (Kaisho / Type KS). Nations are displayed by flag, each linked to their respective national naval warfare listing.
National flag of modern Japan

[ Imperial Japan ]
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Image of the HIJMS RO-100 (Kaisho / Type KS)
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Mission Roles
Some designs are single-minded in their approach while others offer a more versatile solution to seaborne requirements.
Some designs stand the test of time while others are doomed to never advance beyond the drawing board; let history be their judge.
Going Further...
HIJMS RO-100 (Kaisho / Type KS) Short-Range Coastal Submarine appears in the following collections:
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