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Here at LSOZI, we are going to take off every Wednesday for a look at the old steam/diesel navies of the 1833-1946 time period and will profile a different ship each week. These ships have a life, a tale all their own, which sometimes takes them to the strangest places. – Christopher Eger

Warship Wednesday, Jan 8, 2020: Maru Floatplane Carriers

Here we see the Kamikawa Maru-class cargo ship, Kimikawa Maru, converted to a Tokusetsu Suijokibokan (special seaplane carrier) of the Imperial Japanese Navy, at Oominato in northern Honshu, in late 1942. As you can tell, this interesting ship and her sisters could carry a serious load of armed, and often very effective, floatplanes.

Constructed in the late 1930s through a joint endeavor of the Japanese shipping firm Ōsaka Mercantile and Kawasaki Kisen in the latter’s Kobe-based shipyard, the five 6,800-ton ships of the class were intended for the Japan-New York route, a trip of some 15,000 nautical miles. This was no sweat as, using a single efficient MAN-designed Kawasaki-made diesel, they had an incredible 35,000nm range at 17 knots.

However, these ships were also ready to chip in should the Empire require it.

As noted in ONI 208-J, the U.S. Navy’s 400+ page WWII intelligence book on the 1,300 assorted Japanese merchant ships over 1,000-tons:

Modern Japanese merchant ship design provides for deck-gun positions up to 5-inch or 6-inch caliber, the largest pieces being hand-loaded under service conditions. Heavier framing and plating and large diameter stanchions (extending down through two decks) are built in integral parts of the hull to support these positions. Ventilator trunks are conveniently arraigned close by for rapid conversion to ammunition hoists. These trunks always lead to specially prepared watertight compartments suitable for use as magazines. Dual-purpose 3-inch guns and anti-aircraft machine guns are often mounted in rows on lateral platforms.

As such, the U.S. Navy was very interested in these ships on the lead-up to the war, with several high-res images of these vessels taken in the 1930s as they transited the Panama Canal, still located in the ONI’s files.

With Japan increasingly embroiled in the conflict in China, the Kimikawa Maru-class vessels were soon called up for service, many years before Pearl Harbor.

Notably, four out of the five– Kamikawa Maru, Kiyokawa Maru, Kimikawa Maru, and Kunikawa Maru (nothing confusing about that) were converted to armed seaplane carriers, capable of carrying more than a dozen such single-engine floatplanes aft, for which they had two catapults installed to launch them and large boom cranes for recovery. They would also be equipped with as many as six 4.7- or 5.9-inch guns as well as several smaller AAA mounts and machine guns.

Alternatively, twice that many aircraft could be carried stowed below, to be assembled and deployed at some far-off port or atoll if need be. Four similar Mitsubishi-built freighters– Noshiro Maru, Sagara Maru, Sanuki Maru, and Sanyo Maru— were also converted but could only carry about eight seaplanes each. Subsequently, these less successful vessels would be re-rated to transports by 1942.

Notably, many of the IJN’s carrier commanders and admirals learned their trade on these special seaplane carriers to include RADMs Ando Shigeaki, Hattori Katsugi, Shinoda Tarohachi, Matsuda Takatomo, Hara Seitaro, and Yokokawa Ichihei; VADMs Arima Masafumi, Yamada Michiyuki, and Omori Sentaro.

In the late 1930s, their airwing would include Kawanishi E17K (Alf) and Nakajima E8N Type 95 (Dave) scout aircraft, primitive single-float biplanes that couldn’t break 175 knots and carried just a few small bombs and a couple machine guns for self-defense. These would later be augmented by planes like the Mitsubishi F1M2 Pete.

By 1942, this airwing would grow to as many as 14 much more capable Aichi E13A Type Zero (Jake) armed reconnaissance planes and four Daves– the airwing Kamikawa Maru took to Alaska during the Midway operation. Later types like the Nakajima A6M2-N (Rufe) Type 2 Sui-Sen (‘Rufe’) floatplane version of the Zero fighter soon joined them.

At least four Japanese navy pilots chalked up at least three kills while at the controls of floatplanes, most in the A6M-2N: CPO Shigeji Kawai, WO Kiyomi Katsuki, CPO Keizo Yamaza, and CPO Maruyama, although it should be noted that Katuski downed his first aircraft, a Dutch KNIL PBY, while flying an F1M2 Pete. Katsuki, who had 16 kills, spent at least some of his time flying from Kamikawa Maru.

Their tail codes:

• Kamikawa Maru– ZII (15 November 1940) ZI (September 1941) Z (May 1942) YI (14 July 1942)
  L-1 (1943)
• Kunikawa Maru– YII tail code (November 1942) L-2 (January 1943)
• Kiyokawa Maru– R (1941) RI (14 July 1942–November 1942)
• Kimikawa Maru– X (December 1941) C21 (1943)

Once the big balloon went up in December 1941, these four freighters-turned-carriers were used extensively across the Pacific.

Kamikawa Maru would participate in the Malaya campaign and the Battle of the Coral Sea then sail with the fleet for Midway, going on to play a big part in the Aleutians campaign. She would then switch to the Guadalcanal Campaign, and be sent to the bottom by torpedoes from USS Scamp (SS-277) northwest of Kavieng, New Ireland in May 1943.

Kiyokawa Maru helped capture Guam and Wake Island in December 1941, then was later rerated as a transport. She was ultimately sunk in an air raid at Kaminoseki in 1945 but was later raised and returned to a brief merchant career.

Kimikawa Maru, like her sister Kamikawa Maru, would take part in the Midway and Aleutian campaign in 1942-43. A line would be drawn through her name on Poseidon’s ledger in October 1944 after an encounter with the submarine USS Sawfish (SS-276) off Luzon’s Cape Bojeador.

Kunikawa Maru would go on to live through a myriad of actions in the Solomons, including the Battle of Santa Cruz Island, and assorted convoy duties until she hit a mine off Balikpapan in March 1944 and was never the same again. She would be finished for good by an airstrike in May 1945 in that Borneo port.

By the end of the war, all of the K-Marus had been sunk and their planes either shot down, abandoned or otherwise captured.

In all, the K-Maru carriers were an interesting concept, a quick and easy way to send a small expeditionary airwing to sea short of converting the ships to more proper escort carriers such as done by the Allies.

A very interesting postwar interrogation of CDR Kintaro Miura, Kamikawa Maru‘s senior air officer from the outbreak of war until December 1942, is in the NHHC archives.

Several scale models of these vessels and their aircraft are in circulation, as is their accompanying artwork, and they have sparked the imagination of warship fans the world over.

Specs:

Displacement: 6,863 tons standard
Length: 479 feet
Beam: 62 feet
Draft: 30 feet
Installed power: 7,600 shp
Propulsion: 1 Kawasaki-M. A. N. diesel, 1 shaft
Speed: 19.5 knots, 17 in military service
Armament: 2 x 5.9-inch, 2 x Type 96 25 mm (0.98 in) AA, 2 x 13.2 mm (0.52 in) MG
Aircraft carried: 12-18 seaplanes (24 stored)
Aviation facilities: Two catapults, cranes

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