Take Ichi Convoy - Background

Background

In September 1943, the Imperial Japanese Navy (IJN) and Imperial Japanese Army (IJA) agreed to establish defensive positions along what was termed Japan's "absolute zone of national defense". The zone's perimeter reached from the Marianas Islands and Caroline Islands to western New Guinea and the Banda and Flores Seas. At this time there were few Army units in the area, and it was decided to move combat units from China and Manchuria to protect the air bases which formed the basis of Japan's defensive plans. The movement of these troops was delayed by shipping shortages, however. Efforts to reinforce the Marianas and Caroline islands were assigned the highest priority, and the units selected for western New Guinea remained in China until April 1944, when ships became available to transport them.

By early 1944, Allied submarines were sinking large numbers of Japanese ships. Their activities were frequently guided by 'Ultra' intelligence relating to ship movements which was collected by intercepting and decrypting encoded radio transmissions. The IJN routinely broadcast the location and intended route of convoys under its protection, and decrypting these messages allowed Allied naval commanders to alert submarines in the vicinity of convoys. The submarine commanders were free to plan their interception and attack where conditions were most favorable.

The IJN's faulty anti-submarine doctrine also contributed to Japan's shipping losses. The Navy had placed a low priority on protecting merchant shipping from submarine attack before and during the early years of the war and convoys were not routinely assembled until 1943. The Grand Escort Headquarters was formed in late 1943 to coordinate convoys and implement a standard doctrine. The Escort-of-Convoy headquarters was also established in April 1944 to provide a pool of senior commanders who were available to command convoys, though none had any experience with convoy operations or anti-submarine warfare.

Attacks on merchant shipping during February 1944 led the Japanese to change the composition of their convoys. During this month, over ten percent of the Japanese merchant marine was sunk by submarines and air attack. These losses included several transport ships carrying reinforcements to the Marianas and Carolines. In response, the Grand Escort Fleet Headquarters increased the average size of Japanese convoys from five ships to "large" convoys of 10-20 vessels. This change allowed the IJN to allocate more escort ships to each convoy and it was hoped that conducting fewer convoys would also reduce the number of targets available to submarines. While Japanese officers attributed a drop in sinkings during March to the changed tactics, this was actually due to the U.S. Pacific Fleet's submarines being diverted to support raids conducted by the Fast Carrier Task Force that month.

The Take Ichi convoy was assembled at Shanghai in April 1944. Its task was to carry the 32nd Division to Mindanao and the main body of the 35th Division to western New Guinea. Both divisions had been formed in 1939 and were veterans of fighting in China during the Second Sino-Japanese War. One of the 35th Division's three infantry regiments was detached from the division in early April and sent to the Palau islands, arriving there later that month without loss.

The two divisions embarked on large transport ships protected by an unusually strong escort force. Rear Admiral Sadamichi Kajioka—who was a veteran of several previous operations, including the Battle of Wake Island—was appointed to command the convoy. The escort force was the newly established 6th Escort Convoy Command and included Kajioka's flagship, the coal burning minelayer Shirataka, as well as destroyers Asakaze, Shiratsuyu and Fujinami, frigate Kurahashi, ocean escort ships ('kaibokan') CD-20 and CD-22, minesweeper W-2, subchasers CH-37 and CH-38 and gunboats Uji, Ataka and Tama Maru No. 7.