Promoted to sergeant in March 1942, McHugh joined Company C, 1st Battalion 1st Marines and that June sailed aboard the from San Francisco for World War II. His unit was attached to the 1st Marine Division and took part in the Guadalcanal, Cape Gloucester and Peleliu campaigns. He rose to platoon sergeant and gunnery sergeant prior to his return to the United States in November 1944. He was awarded the Purple Heart for wounds suffered in the Peleliu operation.