Second-generation Japanese Americans (Nisei) and other individuals of Japanese descent were officially banned from serving in the U.S. Navy, Marines, Coast Guard, and Army Air Corps for the majority of the war.

Link: https://www.archives.gov/research/aapi/ww2/military

The vast majority of the approximately 33,000 Japanese Americans who served in the U.S. military during WWII served in the U.S. Army — most notably in the 100th Infantry Battalion and the 442nd Regimental Combat Team in Europe, as well as the Military Intelligence Service (MIS) in the Pacific.