|Born||21 July 1886
Kagoshima prefecture, Japan
|Died||12 April 1948 (aged 61)|
|Allegiance||Empire of Japan|
|Service/branch||Imperial Japanese Army|
|Years of service||1906-1945|
|Commands held||Yasuoka Detachment|
|Battles/wars||Soviet-Japanese Border Wars
Second Sino-Japanese War
World War II
|Other work||Japanese governor of Surubaya|
Yasuoka was a native of Kagoshima Prefecture, and graduated from the 18th class of the Imperial Japanese Army Academy in 1906 and from the 26th class of the Army Staff College in 1914. After serving in a number of staff positions, he was assigned to the IJA 51st Infantry Regiment, rising to become its commander by 1922. The following year, he became Chief of Staff of the IJA 9th Division, and that of the IJA 16th Division in 1927.
After having served as commander of the IJA 49th Infantry Regiment from 1930–1932, Yasuoka was transferred to be Chief of Staff of the IJA 5th Division in 1932. In 1935, Yasuoka was promoted to major general and given command of the IJA 30th Infantry Brigade. After having served two years (1936 and 1937) as Commandant of the Armored Warfare School, Yasuoka was promoted to lieutenant general and was made commander of the IJA 1st Independent Mixed Brigade.
With the start of the Second Sino-Japanese War, Yasuoka's expertise in armored warfare was recognized when he was made commander of the Yasuoka Detachment, an armored task force of the Kwantung Army, organized for the Japanese July 1939 offensive of the Battle of Khalkhin Gol. However, the Japanese army suffered a ruinous defeat at the hands of the combined Soviet-Mongolian forces and Yasuoka was relieved of command on 9 July 1939 and his detachment was dissolved.
Yasuoka was assigned command of the 3rd Depot Division to 1941, whereupon he resigned from the Army and officially retired.
In 1942, Yasuoka agreed to accept the post of military-governor of Surabaya in Japanese-occupied Java, Netherlands East Indies. He held the post until the surrender of Japan in August 1945, whereupon he was arrested by Dutch authorities and tried before a military tribunal for war crimes. He was condemned to death and hanged on 12 April 1948.
- Coox, Alvin (1990). Nomonhan: Japan Against Russia, 1939. Stanford University Press. ISBN 0-8047-1835-0.
- Ammenthorp, Steen. "Yasuoka Masatake, Lieutenant-General". The Generals of World War II.
- Ammenthorp, The Generals of WWII
- Coox, Nomonhan