was a

lieutenant general Lieutenant general (Lt Gen, LTG and similar) is a military rank used in many countries. The rank traces its origins to the Middle Ages, where the title of lieutenant general was held by the second-in-command on the battlefield, who was norma ...

in the

Imperial Japanese Army The Imperial Japanese Army (IJA; , ''Dai-Nippon Teikoku Rikugun'', "Army of the Greater Japanese Empire") was the principal ground force of the Empire of Japan from 1871 to 1945. It played a central role in Japan’s rapid modernization during th ...

World War II World War II or the Second World War (1 September 1939 – 2 September 1945) was a World war, global conflict between two coalitions: the Allies of World War II, Allies and the Axis powers. World War II by country, Nearly all of the wo ...

Biography

Military career

Yasuoka was born in Sendai city,

Kagoshima Prefecture is a Prefectures of Japan, prefecture of Japan located on the island of Kyushu and the Ryukyu Islands. Kagoshima Prefecture has a population of 1,527,019 (1 February 2025) and has a geographic area of 9,187 Square kilometre, km2 (3,547 Square m ...

(present day

Satsumasendai, Kagoshima 290px, Satsumasendai City Hall is a city located in Kagoshima Prefecture, Japan. , the city had an estimated population of 90,918 in 46610 households, and a population density of 130 persons per km2. The total area of the city is . History Sa ...

) and was the son of an officer in the Imperial Japanese Army. After attending military preparatory schools in Kumamoto, he graduated from the 18th class of the

Imperial Japanese Army Academy The was the principal officer's training school for the Imperial Japanese Army. The programme consisted of a junior course for graduates of local army cadet schools and for those who had completed four years of middle school, and a senior course f ...

in 1906. After attending the Army Toyama School, he graduated 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. He served n the staff of the

IJA 9th Division The was an infantry division in the Imperial Japanese Army. Its tsūshōgō code name was the or 1515 or 1573.Madez, ''Japanese Armed Forces Order of Battle, 1937–1945'', p. 35. The ''9th Division'' was one of six infantry divisions newly ra ...

, the IJA 29th Infantry Regiment and the

IJA 16th Division The was an infantry division in the Imperial Japanese Army. Its tsūshōgō code name was the , and its military symbol was 16D. The 16th Division was one of four new infantry divisions raised by the Imperial Japanese Army in the closing stages o ...

and after his promotion to colonel in August 1930, as commander of the IJA 49th Infantry Regiment from 1930. In January 1935, he became

Chief of Staff The title chief of staff (or head of staff) identifies the leader of a complex organization such as the armed forces, institution, or body of persons and it also may identify a principal staff officer (PSO), who is the coordinator of the supportin ...

of the

Hiroshima is the capital of Hiroshima Prefecture in Japan. , the city had an estimated population of 1,199,391. The gross domestic product (GDP) in Greater Hiroshima, Hiroshima Urban Employment Area, was US$61.3 billion as of 2010. Kazumi Matsui has b ...

-based

IJA 5th Division The was an infantry division of the Imperial Japanese Army. Its call sign was the . The 5th Division was formed in Hiroshima in January 1871 as the , one of six regional commands created in the fledgling Imperial Japanese Army. Its personnel w ...

. Yasuoka was promoted to major general and given command of the IJA 30th Infantry Brigade in March 1935. He served as commandant of the Army Tank School from August 1936. In March 1938, he was promoted to

and was made commander of the

IJA 1st Independent Mixed Brigade The 1st Independent Mixed Brigade or 1st Mixed Brigade (獨立混成第1旅團) was an experimental combined arms formation of the Imperial Japanese Army. In July 1937, at the beginning of the Second Sino-Japanese War, the brigade was known as the S ...

. With the start of the Soviet-Japanese Border Wars, Yasuoka's expertise in

armored warfare Armoured warfare or armored warfare (American English; see spelling differences), is the use of armoured fighting vehicles in modern warfare. It is a major component of modern methods of war. The premise of armored warfare rests on the abil ...

was recognized when he was made commander of the Yasuoka Detachment, an armored task force of the

Kwantung Army The Kwantung Army (Japanese language, Japanese: 関東軍, ''Kantō-gun'') was a Armies of the Imperial Japanese Army, general army of the Imperial Japanese Army from 1919 to 1945. The Kwantung Army was formed in 1906 as a security force for th ...

, organized for the July 1939 offensive of the

Battle of Khalkhin Gol The Battles of Khalkhin Gol (; ) were the decisive engagements of the undeclared Soviet–Japanese border conflicts involving the Soviet Union, Mongolia, Japan and Manchukuo in 1939. The conflict was named after the river Khalkhin Gol, which p ...

. However, the Japanese army suffered a ruinous defeat at the hands of the combined Soviet-Mongolian forces and Yasuoka was relieved of command in July 1939 and his detachment was dissolved. He was placed in command of the reserve IJA Third Depot Division in August 1939, and went into the reserves in March 1941. He retired from the military at the end of the same month.

Governor of Surabaya

In July 1942, Yasuoka agreed to accept the post of governor of

Surabaya Surabaya is the capital city of East Java Provinces of Indonesia, province and the List of Indonesian cities by population, second-largest city in Indonesia, after Jakarta. Located on the northeastern corner of Java island, on the Madura Strai ...

in Japanese-occupied

Java Java is one of the Greater Sunda Islands in Indonesia. It is bordered by the Indian Ocean to the south and the Java Sea (a part of Pacific Ocean) to the north. With a population of 156.9 million people (including Madura) in mid 2024, proje ...

Netherlands East Indies The Dutch East Indies, also known as the Netherlands East Indies (; ), was a Dutch Empire, Dutch colony with territory mostly comprising the modern state of Indonesia, which Proclamation of Indonesian Independence, declared independence on 17 Au ...

. During his time in Surabaya, he learned enough of the

Javanese language Javanese ( , , ; , Aksara Jawa, Javanese script: , Pegon script, Pegon: , IPA: ) is an Austronesian languages, Austronesian language spoken primarily by the Javanese people from the central and eastern parts of the island of Java, Indones ...

to be able to make a speech in public, and was known for visiting school and government offices without notice. He attempted to employ as many native Indonesians in government positions as possible, both from a practical standpoint, but also from a belief that the Netherlands East Indies should be freed from colonial rule. He also released many of the Dutch officials who were held as prisoners of war to train the Indonesians to take their places. He held the post until the

surrender of Japan The surrender of the Empire of Japan in World War II was Hirohito surrender broadcast, announced by Emperor Hirohito on 15 August and formally Japanese Instrument of Surrender, signed on 2 September 1945, End of World War II in Asia, ending ...

in August 1945, whereupon he was arrested by Dutch colonial authorities and tried before a

military tribunal Military justice (or military law) is the body of laws and procedures governing members of the armed forces. Many nation-states have separate and distinct bodies of law that govern the conduct of members of their armed forces. Some states us ...

where he was declared guilty of unspecified

war crime A war crime is a violation of the laws of war that gives rise to individual criminal responsibility for actions by combatants in action, such as intentionally killing civilians or intentionally killing prisoners of war, torture, taking hostage ...

s. He was condemned to death and hanged on 12 April 1948.

References

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External links

Footnotes

{{DEFAULTSORT:Yasuoka, Masaomi 1886 births 1948 deaths Executed military leaders Military personnel from Kagoshima Prefecture Imperial Japanese Army generals of World War II Members of the Kwantung Army Japanese people executed for war crimes People executed by the Netherlands by hanging Japanese people executed abroad History of Surabaya