Fifty years after the formation of the 100th Infantry Battalion, 3,147 men were listed by Club 100, the 100th veterans’ organization, as having served in the battalion. The original contingent of officers and enlisted men who had sailed from Honolulu in June 1942 numbered 1,432.
While the vast majority of enlisted men were of Japanese ancestry, there were about 20 who had one parent of Japanese heritage while the other was Hawaiian, Portuguese, Chinese or Filipino. There were two Korean Americans who joined the 100th while they were training on the mainland. One enlisted man of Hawaiian ancestry accompanied his half- brother who was Japanese-Hawaiian and had joined the battalion.
According to Masayo Duus in “Unlikely Liberators: The Men of the 100th and 442nd” (1983), four mainland born Japanese joined the 100th at Camp McCoy. Later at Camp Shelby, a Korean American officer from Los Angeles arrived who would become one of the outstanding officers of the battalion.
After the 100th entered combat in September 1943 and casualties increased, replacements of enlisted men were Japanese American volunteers from Hawaii and the mainland. Most trained with the 442nd, but some men had been assigned to other Army units and then were transferred to the 100th. Of the almost 3,150 men who served in the 100th, about 15% were from the mainland. This figure was derived from the different Army Serial Number (ASN) assigned to those inducted on the mainland.