Tokusetsu-Kosakubu

(Pacific Theater of Operations - 1941 -1942)

History of Japanís Overseas Naval Construction and Repair Departments
by Bob Hackett

© 2016-2017 Bob Hackett
Revision 3


On 8 December 1941, following its meticulously laid three-phase plan for the conquest of the Pacific and seizure of the regionís vital strategic resources, Japan unleashed its military forces led by its powerful Imperial Navy. At that time, the IJN consisted of 10 battleships, 6 fleet carriers, 4 light carriers, 18 heavy cruisers, 20 light cruisers, 112 destroyers, and 65 submarines plus a substantial number of smaller escort, mine warfare, auxiliaries and tenders. At that time, Japan needed some 10 million tons of merchant shipping to meet its requirements, but had little more than 6 million tons under its own flag.

In the first phase of its three-phase plan, Japan planned, within the coming five-months, to eliminate its major naval rival for the control of the Pacific, the United States Pacific Fleet, based at Pearl Harbor. The Japanese plans also called for the elimination of potential opposition on Guam, Wake and the Gilberts . Further, their plans called for the invasion and occupation of the Philippines, Britain's Crown Colony of Hong Kong, plus Thailand, oil-rich British Borneo, Sarawak and northern Malaya.

The second phase of Japanís Pacific War plans called for the conquest of Malaya and the British Straits Settlement at Singapore, southern Burma (Myanmar) and the Bismarcks, while the third and final phase called for the seizure of the crown jewel, the Netherlands East Indies and its oil and other critical natural resources, all the while securing the rest of Burma.

These conquests came with serious consequences to the IJN. Only hours after the attack on Pearl Harbor, the US Navy issued orders to engage in unrestricted submarine warfare against Japan. This combined with the USNís aviation successes at Coral Sea and Midway and attacks on Japanís military installations in the Pacific slowly began to take its toll on the IJN.

This series will cover Japanís major overseas ship repair units (Naval Construction and Repair Departments) (Tokusetsu-Kosakubu) set up by the IJN Naval Facility Command (Kaigun Shisetsu Honbu) in the Sino-Japanese War to handle repairs of damaged vessels that otherwise would have had to be taken out of the war to return to the homeland for repairs or abandoned. After the outbreak of the Pacific War, captured Allied ship repair facilities were likewise added.

This series will NOT cover mainland Japan's major naval bases at Kure, Yokosuka, Sasebo and Maizuru and Ominato, all of which had their own navy yards (Kaigun Kosho). Japanese ship repair facilities in territories of Formosa (Taiwan) at Kirun (Keelung) and Takao (Kaohsiung/Gaoxiong) and Korea at Chinkai (Chinhae) and at Dairen (former Port Arthur), Manchukuo (Manchuria), likewise will not be covered.

The American submarine fleet achieved its first significant results during its interception of Japanese transports carrying reinforcement troops and supplies to Guadalcanal. As the war progressed, Japan's merchant shipping position collapsed despite that the output of Japanese shipbuilding yards more than doubled their prewar estimated maximum capacity, because losses also were more than double earlier estimates. The shipyards' output figures were misleading. The unprecented level of ship building only was made possible by denial to existing shipping of overhauls, repairs and refits. The continual postponement of maintenance and repairs only increased the ultimate need for repairs. By 1944, over 9.5 millions tons of merchant shipping underwent some sort of maintenance and by 1945 yard space devoted to reconditioning jumped another 50 percent. By the time of its surrender, over half of the Japanese merchant fleet was awaiting servicing.

The Empire of Japan was totally dependent upon the sea for transporting its troops and war materials to far-flung theaters of war across the Pacific, yet the most serious weaknesses in the IJN were not readily apparent. They were its merchant fleet and its shipyards, both of which were alarmingly inadequate when measured against Japanís immediate and long term requirements. The military consequences of the demise of the merchant fleet were direct and persistent. Japan's armed forces were unable to ship sufficent quantites of munitions, arms, foodstuffs, fuel and reinforcements to sustain their front lines of battle. Failure to maintain an adequate maritime transport system also debilitated the war effort at home as imports of strategic raw materiels and fuel fell off.

The USN's Bureau of Ornance's (BuOrd) tight "Gun Club" bureaucracy of senior officers and top civil servants gave the IJN a wartime respite because of BuOrd's arrogant refusal to address the root causes of the poor performance of the submarines' Mark 14 steam torpedo. Rather than conducting rigorous examinations of the torpedoes, BuOrd instead took an institutional defensive position and blamed their product's - the Mark 14's - many failures on their customers - the submarines' operators.

It took BuOrd over two years, with help from SUBPACFLT operators, to correct the Mark 14's shortcomings including its running deeper than set, circular running, depth control failures and defective detonators (both contact and magnetic types). But Japan wasted the unintended respite to correct many doctrinal and technological problems such as anti-submarine and anti-mine counter measures, inadequate quality and quantity of its escort forces and other problems. As a result, by 1944 the USN's submarine fleet recovered and then savaged Japan's merchant shipping fleet. By August 1945, only 1.5 million tons remained of a fleet that had totaled 6.4 million tons prewar.

The major Japanese overseas Naval Construction and Repair Departments (ship repair units) this series will cover were located at:

No. 1 Naval Construction and Repair Department at Shanghai, China. (Posted 9/1/2016)

No. 2 Naval Construction and Repair Department at Hong Kong, BCC. (Posted 10/1/2016)

No. 4 Naval Construction and Repair Department at Truk, Carolines. (Posted 11/1/2016)

No. 8 Naval Construction and Repair Department at Rabaul, New Britain, Bismarcks.(Posted 12/1/2016)

No. 30 Naval Construction and Repair Department at Palau, Carolines.(Posted 1/1/2017)

No. 101 Naval Construction and Repair Department at Singapore, Malaya.(Posted 2/1/2017)

No. 102 Naval Construction and Repair Department at Surabaya, Java, Netherlands East Indies.(Posted 3/1/2017)

No. 103 Naval Construction and Repair Department at Manila, Philippines.


Author's Note:
[1] The best translation of the term IJN "2nd Ship Repair Unit" according to British Intelligence reports was "No.2 Naval Working Department:" however, according to "Fontessa" a well-respected Japanese contributor to "Axis History Forum" there is a Japanese-English dictionary titled ďJapanese military and technical termsĒ. The Joint Intelligence Center Pacific Ocean Areas (JICPOA) edited this dictionary in last part of the Pacific War to help evaluations of captured Japanese documents. According to it, the English translation of Kaigun Kosakubu is "Naval Construction and Repair Department." This translation will now be used in this series to designate all the IJN's Ship Repair Units. Erich Muehlthaler of Germany also notes that the No.2 Naval Construction and Repair Department was not in charge of all Hong Kong' shipyards, but only controlled several of them.

Thanks go to Sander Kingsepp of Estonia and Erich Muehlthaler.

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

Bob Hackett