Japanese Sea Plane Operations in the Marshall Islands

by Dirk H.R. Spennemann

The atolls of Micronesia are ideally suited for sea-plane operations.Atolls
are rings of coral reef usually with a large and quite calm lagoon in the
middle.  The islands on the windward side of the reefs provide a an ideal plane
anchorage on the leeward beach, sheltered from wind and waves. The lagoon is
usually clam enough to permit unrestricted landing and take-off of larger
flying boats, and so it is not surprising that the lagoons were used as
seaplane bases first by civilian and later by military aviation.

Civilian sea plane operations

A reliable long-range sea-plane, the Kawanishi H6K type 97 flying boat ("Mavis') had become available to the Imperial Japanese Navy in 1936. The sea-plane base were officially operated by a civilian airline, the Dai Nippon Koku K.K. (Greater Japan Airlines) although numerous of its pilots were reserve naval pilots. The first irregular air service flying Yokohama, Saipan and Palau opened in 1935, after successful test flights had been carried out in 1934 . The flights became more frequent in 1937 and a regular air route from Yokohama to Saipan (via Belau) was officially opened in December 1938 or April 1939 with hopes for an eventual extension to Papua New Guinea and Australia. The Annual Report of the South Seas Government, the Japanese administration of Micronesia, for the year 1938 states that the airline Dai Nippon Koku Kaisha began and air service connecting Japan with Saipan and Belau. In 1939 Pohnpei and Jaluit were added. During the Pacific War the Dai Nippon Koku K.K. continued its long-distance services, flying scheduled services on its three routes Yokohama-Saipan-Palau-Timor, Saigon-Bangkok and Yokohama-Saipan-Truk-Ponape-Jaluit.

Military development

By 1937 the Imperial Japanese Navy was calling the shots in Micronesia and initiated construction of major improvements in air, sea and land facilities in Micronesia. Sea-plane facilities had already been built for the Nan'yõ-Cho (South Seas Government) in the late 1930s on several islands of the former Mandated Territory and between 1935 and 1937 the Japanese government spent almost Yen1,000,000 on further construction of air facilities.

The Japanese airroutes in the western Pacific. 1--Yokohama-Saipan-Palau; 2--Palau- Chuuk-Pohnpei-Jaluit; 3--Saipan-Manila; 4--Saipan-Saigon; 5--Palau-Port Moresby-Australia (planned).

The atolls of the Marshall Islands were ideally suited for sea-plane bases. All that was needed to establish a fast seaplane base was to detail a seaplane tender to the atoll, from which the planes could be supplied and serviced. The personnel would sleep in tents on the beach and nor permanent structures needed to be erected. The planes would be beached at a sandy beach. Such seaplane bases could be set up almost ad hoc if the situation demanded it. The development of a float plane version of the successful Mitsubishi A6M Zero fighter meant that advanced fighter bases could be erected ad hoc on any of the atolls of the Eastern Caroline, the Marshall Islands and Kiribati.

A temporary seaplane base could be even set up by the means of one or more supply submarines waiting for the arrival of the flying boats or aircraft. In the Marshall Islands, known seaplane bases with shore facilities were located on Wotje, Wotje Atoll; Ebeye, Kwajalein Atoll; Jabwor, Jaluit Atoll; Djarrit, Majuro Atoll; and Engebi, Enewetak Atoll. Suspected seaplane facilities or temporary seaplane bases may have existed on Rongelap, Mile and Bokak.

Military operations

Long-range seaplanes became available in 1936 with the introduction of the Kawanishi H6K flying boat and in 1942 with the introduction of the Kawanishi H8K flying boat. In addition, single engine float planes were used for anti-submarine patrol. The seaplane base in Jaluit, for example, is known to have harbored in mid-1943 the Mitsubishi A6M2-N's ("Rufe"), a float plane version of the "zero" fighter The aircraft visible on a contemporary photograph possibly represent two air wings and all belong to the 802ndKokutai (Squadron).

The bulk of the military operations of the sea planes constituted the flying of long search patrols in a set search triangle, looking for enemy submarines and surface shipping. The planes were equipped with communications and small anti-submarine bombs. Attack operations were less common:

The Japanese attack on Pearl Harbor on December 8th, 1941, was partially launched from bases in the Marshall Islands. Not only came the submarines providing the submarine screen from the base of the 6th submarine fleet in Kwajalein, but also several flying boats taking part in the Pearl Harbor as well as in the raids on the U.S. bases on Wake I., Howland I. and Canton I. were launched from the seaplane bases of the Yokohama Kokutai (later 802nd Kokutai) on Wotje and Jaluit.

Kawanishi flying boats based at Jaluit and Wotje were also used as long-range bombers and on March 4-5, 1942, bombed Oahu, Hawaii, in retaliation of the U.S. carrier strike against the Marshalls in early February 1943. The French Frigate Shoals, some 700 miles northwest of Hawaii Island, were to be used by the Japanese seaplanes as a rendezvous point with submarines carrying fuel and bombs. The French Frigate Shoals had not been used by the Japanese Fleet as a seaplane base in the 1941 carrier attack on Pearl Harbor which began the Pacific War. Having come into classified U.S.Navy Information with the fall of Wake I. on 23 December 1941, however, the Japanese then possibly decided to utilize the atoll. Refueling and arming of two Kawanishi H8K flying boats took place in the night of 3 March 1942 (U.S. time), which carried out a successful raid on Pearl Harbor the day after.

Another scheduled Japanese rendezvous of three submarines with long-range flying-boats and submarines at French Frigate Shoals had to be called off between May 26th to 31st. The flying-boats were to have reconnoitered Pearl Harbor in preparation for the attack on Midway. Following the Battle of Midway, the U.S. Navy erected a complete Naval Air Station on French Frigate Shoals, which precluded any further Japanese rendezvous.

In September 1942 another major flying boat raid was conducted, attacking the U.S. bases on Funafuti, Tuvalu, and Canton I. It appears that these flying boats either never returned to their home bases in the Marshall Islands or that they were relocated in order to avoid any psychological draw-backs for the 802ND. In addition, flying boats from the Marshall Islands were once more scheduled to bomb Pearl Harbor . As had been the case in March 1942, the French Frigate Shoals were to be used by the Japanese seaplanes as a rendezvous point with a submarine carrying fuel and bombs. However, the Pearl Harbor raid did not eventuate, as the submarine scheduled for a rendezvous with the flying boats found the shoals occupied by a U.S. Naval Air Unit and the rendezvous had to be called off.

As the war progressed, and the U.S. air attacks against the Marshalls become more common, flying boat operations became less frequent, and a number of boats were sunk at their moorings by U.S. fire, such as the three flying boats of Ebeye or the boat off Wotje.

The last Japanese flying boat operations in the Marshall islands occurred in the first and second week of February 1944, when flying boats from the Japanese headquarters in Chuuk flew to the then by-passed bases of Taroa/Maloelap, Wotje and Mile to take off fighter and bomber pilots stranded there.

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Bibliographic citation for this document

Spennemann, Dirk H.R. (1992 [2000]) Japanese Sea Plane Operations in the Marshall Islands. Johnstone Centre of Parks, Recreation and Heritage, Charles Sturt University, Albury. URL: http:/marshall.csu.edu.au/Marshalls/html/WWII/SeaPlaneOps.html
The article first appeared in the Marshall Islands Journal on 25 December 1992

Dirk H.R. Spennemann, Institute of Land, Water and Society, Charles Sturt University, P.O.Box 789, Albury NSW 2640, Australia.
e-mail: dspennemann@csu.edu.au

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