Japanese Thirty First Army
Japanese POWs at Guam at time of the surrender of Japan
Active	February 18, 1944 - August 15, 1945
Country	Empire of Japan
Branch	Imperial Japanese Army
Type	Infantry
Role	Corps
Garrison/HQ	Truk
Engagements	Operation Hailstone Battle of Saipan Battle of Guam

The Japanese 31st Army (第31軍, Dai-sanjyū-ichi gun) was an army of the Imperial Japanese Army during World War II.

History

The Japanese 31st Army was formed on February 18, 1944 under the Imperial General Headquarters as a garrison force to contest landings by Allied forces in the Japanese South Seas Mandate island-by-island, and to inflict such losses in a war of attrition that it would deter an American invasion of the Japanese home islands. The South Seas Mandate was divided into three sections (Northern Mariana Islands, southern Mariana Islands, and Truk). The 80,000 man Japanese 31st Army was initially headquartered on Truk.

After Operation Hailstone, the Japanese garrison on Truk was isolated as American forces continued their advance towards Japan by invading other Pacific islands. Cut off, the Japanese forces on Truk and other central Pacific islands ran low on food and faced starvation before Japan surrendered in August 1945. (Stewart, 1986)

The garrisons in the Marianas were largely annihilated at the Battle of Saipan and Battle of Guam.

Structure

Thirty-First Army

• Southern Marianas Force
  • 29th Infantry Division
  • 48th Independent Infantry Brigade
• Northern Marianas Force
  • 43rd Infantry Division
  • 47th Independent Infantry Brigade
• Truk Garrison Force
  • 52nd Infantry Division
  • 50th Independent Infantry Brigade
  • 51st Independent Infantry Brigade
  • 52nd Independent Infantry Brigade

List of commanders

Commanding officer

Chief of Staff