With the start of the Russo-Japanese War in 1904, Diterikhs became chief officer for special duties at the 17th Army Corps headquarters. He arrived at the front in Manchuria in August 1904, and participated in the Battles of Liaoyang, Shaho and Mukden. By the end of the war, he was a lieutenant. After the end of the war he returned to Moscow, and in 1906 was chief officer for special duties at the 7th Army Corps headquarters. The following year, he had the same position at the Kiev Military District headquarters. He was promoted to colonel in 1909. In 1910, he served as a senior aide at the Kiev Military District headquarters. From 1913, Diterikhs was head of the Mobilization Department of the Main Directorate of the General Staff.