The Japanese 5th Area Army was formed on March 16, 1944 under the General Defense Command as part of the last desperate defense effort by the Empire of Japan to deter possible landings of Allied forces in Hokkaidō, Karafuto/South Sakhalin and the Chishima Islands/Kuriles during Operation Downfall (or Operation Ketsugō (決号作戦, Ketsugō sakusen) in Japanese terminology).

[1]　The 5th Area Army consisted mostly of poorly trained reservists, conscripted students and home guard militia.

Weapons, training, and uniforms were generally lacking: some men were armed with nothing better than muzzle-loading muskets, longbows, or bamboo spears; nevertheless, they were expected to make do with what they had.

[2] After breaking the Soviet–Japanese Neutrality Pact, the Soviet Union invaded Karafuto and the Kuril Islands on August 11, 1945, just four days before the surrender of Japan.

Many surviving soldiers of the 5th Area Army in Karafuto and Chishima became prisoners of war in Siberia and other parts of the Soviet Union until the mid-1950s.