[1] In June 1942, Yokoyama was assigned command of the Manchukuo-based IJA 8th Division, which was garrisoned in eastern Heilongjiang guarding the border with the Soviet Union.

However, in 1944, as the situation in the Pacific War continued to deteriorate for the Japanese, portions of the IJA 8th Division were sent to Truk, where they were largely annihilated by lack of food and American air raids.

The remainder of the division was transferred from Manchukuo to the Philippines under the command of General Yamashita Tomoyuki's 14th Area Army, and under the name of “Shimbu Group”, was wholly made responsible for the defense of southern Luzon.

In July 1953, Yokoyama's death sentence was commuted by President Elpidio Quirino and he was allowed to return to Japan.

[4] In an interview done after his pardon and before his return to Japan, Yokoyama accepted responsibility for what he had allowed to happen and said, "The memory of the destruction and murder committed in the Philippines will remain with me as a nightmare that I will carry to my grave..." He died in 1961.