In September 1911, the prince was enrolled in the second year of the Army Central Youth School, a military preparation school located in Tokyo.
He was poor in gymnastics due to his small statue, but excelled in music and martial arts.
He was then enrolled in the 29th class of the Imperial Japanese Army Academy, from which he graduated on 25 May 1917 with an excellent record.

He was commissioned a second lieutenant in the infantry on 25 December, and steadily rose up the ranks, receiving promotions to lieutenant (April 1920), and captain (July 1923).
He graduated from the 35th class of the Army Staff College in November 1923 and commanded a battalion of the Guards 2nd Infantry Regiment.
He was assigned to the Imperial Japanese Army General Staff Office in December 1924, and to the staff of the Chosen Army in July 1926.
In May 1927, he was sent on an extensive European tour, visiting France, Switzerland, United Kingdom, Belgium, Netherlands, Germany, Denmark, Norway, Sweden, Poland, Austria, Czechoslovakia, Italy, Monaco, and returning to Japan in April 1928.
In August, he was promoted to major and in August 1929 became commander of the IJA 1st Infantry Regiment.
In December 1930, he was assigned to the Inspectorate General of Military Training and was promoted to lieutenant colonel in August 1932.
He became colonel in August 1935 and commanded the Utsunomiya-based IJA 59th Infantry Regiment.
From April 1937, he served as an instructor at the Army Academy.

In July 1938, the prince was promoted to major general and from December was assigned to the staff of the North China Area Army, which was engaged in combat operations in northern China following the start of the Second Sino-Japanese War.
Throughout the first half of 1939, he made extensive inspection tours of front-line units throughout northern Japan, and reviewed Kwantung Army garrison units in Manchukuo.
In August, he was appointed commander of the Guards 2nd Brigade and in May 1940 was commander of the reserve Fourth Depot Division.
He was promoted to lieutenant general in December.
In July 1941, he was appointed commander of the IJA 51st Division.
 
Under his command, the division relocated to Manchukuo to participate in the Special exercise of the Kwantung Army (actually a mobilization for the possible large-scale conflict with the Soviet Union).
The preparations for the war with the Soviet Union were officially cancelled in August 1941.
In September, the division was transferred to Guangdong under command of IJA 23rd Army.
He returned to a post on the staff of the Inspectorate General of Military Training in November.

From August 1942, the prince was transferred to the Imperial Japanese Army Air Force and became commander of the 1st Air Army from July 1943.
In April 1945, he became a member of the  Supreme War Council
In September 1911, the prince was enrolled in the second year of the Army Central Youth School, a military preparation school located in Tokyo. He was poor in gymnastics due to his small statue, but excelled in music and martial arts. He was then enrolled in the 29th class of the Imperial Japanese Army Academy, from which he graduated on 25 May 1917 with an excellent record.
He was commissioned a second lieutenant in the infantry on 25 December, and steadily rose up the ranks, receiving promotions to lieutenant (April 1920), and captain (July 1923). He graduated from the 35th class of the Army Staff College in November 1923 and commanded a battalion of the Guards 2nd Infantry Regiment. He was assigned to the Imperial Japanese Army General Staff Office in December 1924, and to the staff of the Chosen Army in July 1926. In May 1927, he was sent on an extensive European tour, visiting France, Switzerland, United Kingdom, Belgium, Netherlands, Germany, Denmark, Norway, Sweden, Poland, Austria, Czechoslovakia, Italy, Monaco, and returning to Japan in April 1928. In August, he was promoted to major and in August 1929 became commander of the IJA 1st Infantry Regiment. In December 1930, he was assigned to the Inspectorate General of Military Training and was promoted to lieutenant colonel in August 1932. He became colonel in August 1935 and commanded the Utsunomiya-based IJA 59th Infantry Regiment. From April 1937, he served as an instructor at the Army Academy.
In July 1938, the prince was promoted to major general and from December was assigned to the staff of the North China Area Army, which was engaged in combat operations in northern China following the start of the Second Sino-Japanese War. Throughout the first half of 1939, he made extensive inspection tours of front-line units throughout northern Japan, and reviewed Kwantung Army garrison units in Manchukuo. In August, he was appointed commander of the Guards 2nd Brigade and in May 1940 was commander of the reserve Fourth Depot Division. He was promoted to lieutenant general in December. In July 1941, he was appointed commander of the IJA 51st Division.  
Under his command, the division relocated to Manchukuo to participate in the Special exercise of the Kwantung Army (actually a mobilization for the possible large-scale conflict with the Soviet Union). The preparations for the war with the Soviet Union were officially cancelled in August 1941. In September, the division was transferred to Guangdong under command of IJA 23rd Army. He returned to a post on the staff of the Inspectorate General of Military Training in November.
From August 1942, the prince was transferred to the Imperial Japanese Army Air Force and became commander of the 1st Air Army from July 1943. In April 1945, he became a member of the  Supreme War Council
Yi Un