IJN Overseas No.4 Naval Construction and Repair Department

Tokusetsu-Kosakubu

(Battleships YAMATO and MUSASHI at Truk in 1943)

History of the IJN's No. 4 Naval Construction
and Repair Department at Truk, Carolines
by Bob Hackett
© 2016 Bob Hackett

Truk Lagoon forms a rough triangle more than 30 miles on each side. Inside the lagoon are many islands, not coral reefs, of which more than eight are more than one square mile in size. It provided not just sufficient anchorage for a whole Japanese fleet during that era, but also enough area to allow several vessels to maneuver for training. The islands also provided enough room for several airstrips.
When the Imperial Japanese Navy (IJN) occupied Micronesia in World War I, and during the League of Nations mandated administration that followed, the IJN was well aware of Truk’s importance. However, in strict observance of the postwar naval treaties, Japan did little to establish a naval base there. At the outbreak of the Pacific War, there was only one half of a completed airstrip on Takeshima (Bamboo Island), a small island less than 1,000 meters long. There was no underground oil storage, nor any repair facilities on land.
Prewar, the IJN's main concern was for the security of what was to become its main fleet anchorage in the southwest Pacific. The importance of the Truk atoll in the Carolines had grown since a 1939 decision by Japan to form a defensive perimeter to the east of the line of the Marianas into the area of the Gilberts, Ellice and Marshall islands. Truk occupies a key position in the middle Pacific area, able to control Midway to the north, the Marshalls in the east, and Rabaul and New Britain to the south. Because of the need to hold the approaches to Truk from the SE, IJN planners decided to secure Rabaul, an Australian seaplane base in the Bismarcks and taking Lae and Salamaua on the NE coast of Australian New Guinea and Tulagi, an Australian seaplane base in the southern Solomon Islands.
The base at Truk at first did not have substantial repair facilities. On 20 November 1941, Captain/Engineer Yoshii Joichi was appointed Director of the No. 4 Naval Construction and Repair Department and served until 10 November 1942. Even after war began, the IJN was slow to strengthen Truk as a Naval Base. In early 1942, at Truk, IJN repair ship SHOEI MARU provided repairs for light cruiser TATSUTA.
In the summer of 1942, as the United States Navy began its offensive on Guadalcanal and the Solomon Islands became the main theater of fighting. Truk became the center of Japanese naval operations. Almost all IJN naval vessels gathered there before making sorties into the Solomons, and returned to Truk for refueling and repair when damaged. Never before had the need for oil storage and repair facilities been more urgent, and the Japanese Navy concentrated its oil tankers and repair ships there while quickly trying to build such facilities on land as well.
Later in 1942, IJN repair ship URAKAMI MARU started repairs to submarine I-33 supervised by URAKAMI MARU's Kosakubucho (Repair Officer) Cdr/Engineer Yoshitake Naoyuki. I-33 was secured to the wharf on Natsushima (Dublon) Island, but inappropriate actions by I-33’s navigator, then senior officer aboard, resulted in the submarine flooding. I-33 quickly sank killing 33 crewmen.
During May 1942, the 85th Submarine base, was constructed on the western shore of Dublon Island. It serviced, supplied and did minor repairs to subs. Torpedoes were stored in caves and transported by rail car to the shore. Many different repair and barracks existed specific to submarines.
The South Seas Development Company (Nan’yo Kohatsu K.K) had docking facilities on the southwestern tip of Dublon Island. Its supply storage and fish cannery were commandeered by the IJN and it became the Fourth Naval Dockyard. It was the main receiving area for the military. More warehouses and a refrigeration building, HQ, and a two story barracks were constructed. A thousand men worked here on ship repairs, mostly damage sustained to ships from American submarine attacks. The facility also had a 30 ton floating crane and 2,500 ton dry dock. Nearby was a sawmill and small rail cars connected most of the buildings. The Truk Transportation department loaded and unloaded supplies from ships. Since there were no docks for the larger ships, supplies needed to be ferried to the bigger ships. A derrick, carts, 40 trucks, barges, harbor craft, tugs and sampans were used for these purposes.
Truk’s facilities included five airstrips, seaplanes bases, a torpedo boat station, submarine repair shops, a communication center, and a radar station. The main radio station of the five in the islands was located at Dublon Island, where several concrete radior receiver shelters and buildings were constructed. The Fourth Harbor Department was located on the southeastern part of the island near Doblon Town. It was 22 wooden buildings including repair shops, warehouses and barracks. As there were not enough repair facilities on Truk, Japanese naval vessels sometimes had to go all the way back to the homeland for repairs, thus reducing the size of the naval forces available for the Solomons campaign.
Completed in 1940, fleet repair ship AKASHI was the only specifically-designed repair ship built by Japan. She was fully equipped with a tool room, blueprint room, electric repair shop and a machine shop equipped with 114 various machine tools as well as an assembly plant and facilities for casting, forging, welding, copper working and woodworking. AKASHI was also fitted with a 23-ton crane, two 10-ton cranes and two 5-ton cranes fore and aft to transfer repair parts and to handle stores. The Japanese estimated that she alone could carry out 40 percent of the repairs needed by the Combined Fleet.
AKASHI performed yeoman work to minimize the deficiences in repair facilities on Truk. In 1942, AKASHI's Kosakubucho Captain/Eng Masuda Nihei and Captain/Eng Masuda Nihei and Captain/Eng Yamauchi Shojiro supervised varying degrees of repairs at Truk by AKASHI for fleet carrier SHOKAKU, light carrier ZUIHO, escort carrier TAIYO, cruisers CHIKUMA and MOGAMI, light cruisers ISUZU and JINTSU, seaplane tender CHITOSE and destroyers AMATSUKAZE, ARIAKE, ASAGUMO, ASASHIO, HAGIKAZE, IKAZUCHI, KAGERO, KUROSHIO, MINEGUMO, MURASAME, SAMIDARE, SHIRATSUYU, SHIRAKUMO, TERUZUKI, URAKAZE and YUGIRI and auxiliary patrol boat KIMPO MARU No. 1. Most of the damages to these ships occurred in actions in the Solomons.
On 10 November 1942, Captain/Eng Takagi Eiji was appointed Director of the No.4 Naval Construction and Repair Department and served until 10 March 1943.
It was not until the summer of 1943 that the Japanese Navy began to construct three more airstrips at Truk, two on Harushima (Spring Island) and one of Kaedeshima (Maple Island). On 1 November 1943, Rear Admiral/Eng Aoki Masao (24) was appointed Director of the No.4 Naval Construction and Repair Department and served until 10 May 1944.
In 1943, among the warships that received varying degrees of repairs at Truk by AKASHI were battleship YAMATO, cruisers AOBA, KUMANO and MAYA, light cruisers AGANO, NAGARA, SENDAI, destroyers AKIZUKI, AMAGIRI, ARASHIO, ASASHIO, FUMIZUKI, HAMAKAZE, HARUSAME, HATSUKAZE, ISOKAZE, KAGERO, KAWAKAZE, MAIKAZE, MICHISHIO, NAGANAMI, NOWAKI, OYASHIO, SAMIDARE, SHIRATSUYU, SUZUKAZE and UZUKI, seaplane tenders KAMIKAWA MARU and SANYO MARU, submarine I-180, fleet tanker HOYO MARU, oiler (ex-seaplane tender) NOTORO, auxiliary aircraft transport KEIYO MARU, armed merchant cruiser AIKOKU MARU, cable layer OSEI MARU and transports NANKAI MARU and (ex-AMC) NOSHIRO MARU. Again, most of the damages to these ships occurred in actions in the Solomons. The repairs to these ships were conducted throughout the year, and were supervised by AKASHI's succesive 1943 Kosakubucho: Captain/Eng Yamauchi Shojiro, Captain/Eng Tomita Ichiro and Captain/Eng Kubo Tokuichi.
On 10 March 1943, Captain/Eng Uchida Tadao was appointed Director of the No.4 Naval Construction and Repair Department and served until 1 November 1943.
Also in 1943, IJN repair ship HAKKAI MARU's Kosakubucho Captain/Eng Omoto Masazo, Captain/Eng Sakagami Masanobu and Cdr/Eng Shimizu Yoshitaka supervised repairs at Truk for ammunition supply ship KIKUKAWA MARU, transport OKITSU MARU and to IJN repair ship YAMASHIMO MARU, undoubtedly closely watched by YAMASHIMO MARU's own Kosakubucho, Cdr/Eng Yamamoto Ryozai.
The concentration of oil tankers in Truk disrupted the flow of oil from Southeast Asia back to the Japanese homeland. Even super battleships YAMATO and MUSASHI served as tankers, supplying fuel to smaller warships instead of engaging in combat operations.
On 1 November 1943, Rear Admiral/Eng. Aoki Masao (24) was appointed Director of the No. 4 Naval Construction and Repair Department and served until 10 May 1944.
In 1944, among the warships that received varying degrees of repairs at Truk supervised by AKASHI's Kosakubucho Captain/Eng Kubo were light cruiser AGANO and ex-armed merchant cruiser KIYOSUMI MARU. In early January 1944, AKASHI was ordered to steam from Truk to Saipan to provide emergency repairs for torpedoed escort carrier UNYO. By the end of the month, AKASHI completed the repairs and UNYO departed Saipan for Yokosuka escorted by three destroyers. AKASHI then returned to Truk.
On 17 February 1944, Vice Admiral (later Admiral) Marc A. Mitscher's (former CO of HORNET, CV-8) Task Force 58's five fleet carriers and four light carriers, supported by six battleships, ten cruisers and 28 destroyers launched Operation "Hailstone" and attacked airfields, and shore installations on Truk and ships in the lagoon. AKASHI was anchored in Truk's Repair Anchorage located W of Dublon and N of Fefan Islands. At the time of Task Force 58's raids, destroyers FUMIZUKI and KIYOSUMI, YAMAGIRI, HOYO and KENSHO MARUs and TONAN MARU NO. 3 were in this anchorage waiting or undergoing repairs. Prior to the raids, AKASHI probably performed repairs on most, or all, of these ships.
During the two days of the raid, TF 58 sank 31 transports and 10 naval vessels (two cruisers, four destroyers and four auxiliary vessels) and damaged severely about 100 more, 26 transport ships and 3 oil tanks, destroys 2,000 tons of food, and more than 180 airplanes, of which more than 100 were lost on the ground. Truk is eliminated as a major fleet anchorage for the IJN.
At 0400, on 20 February 1944, AKASHI departed Truk for Palau with destroyers AKIKAZE and FUJINAMI in the Combined Fleet's redeployment. AKASHI's speed was reduced to 12 knots by damage sustained in the raids.
TF 58’s raids on Truk, together with the loss of the Gilberts and Marshalls, suddenly lessened the importance of Truk as a naval base. The Combined Fleet, moved westward from Truk into the Carolines, Singapore, and even the homeland. Soon afterward, the Japanese Navy withdrew its land-based aircraft to the Marianas and western Carolines. Truk was no longer a vital naval base, just a stepping stone between the Marianas and Rabaul.
The bad situation on Truk got worse when U.S. forces invaded the Marianas in June 1944. Truk could contribute little to the Japanese defense, and the fall of the Marianas left Truk largely isolated, except for very few small visits by submarines and flying boats. From that time on, Japanese forces on Truk had to endure not just Allied air attacks, but mounting starvation and disease until the war ended in August 1945.
On 10 May 1944, Captain/Eng Harada Kenshiro was appointed Director and Chief Engineer of the No. 4 Naval Construction and Repair Departmentt and served until 1 July 1944.
On 1 July 1944, Captain/Eng Morita Teizo (27) was appointed Director and Chief Engineer of the No. 4 Naval Construction and Repair Department and served until 10 October 1944 when he was appointed the additional duty of Chief Eng, 4th Fleet. On 1 May 1945, he was promoted Rear Admiral/Eng and served until the war's end.

Author's Notes:
Thanks go to Fontessa-san of Japan, on "Axis History Forum" for the incredible amount of work he went to combing through the (Kaigun Jirei Koho) Naval Transfer and Promotion Lists and JACAR to find the Directors of the IJN's Naval Construction and Repair Departments. Thanks also to Sander Kingsepp of Estonia.

Questions to the author concerning these TROMs should be posted on the Discussion & Questions board.

-Bob Hackett

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