 He enlisted in the United States Marine Corps Reserve on January 13, 1942.Serving in the Guadalcanal Campaign during World War II, Private First Class Larson was killed in action on Guadalcanal on October 8, 1942, while attempting to swim the Matanikau River under heavy Japanese fire to rescue a wounded comrade (see Actions along the Matanikau).Larson was posthumously awarded the Silver Star for his selfless courage, and shared in the Presidential Unit Citation awarded the 1st Marine Division for its actions on Guadalcanal.