Upon the outbreak of World War II, Gilormini offered his services to the Royal Air Force and served with them. As a member of the RAF, he flew in a squadron of P-39s from England to North Africa and participated in the Allied invasion of Oran. He served with the RAF until November 30, 1942, when he joined the United States Army Air Forces with the rank of second lieutenant. In October 1942, he was assigned to the 346th Fighter Squadron and flew the Bell P-39 Airacobra interceptor. In March 1943, he was transferred to the 345th Fighter Squadron of the 350th Fighter Group in North Africa and Italy, to replace pilot losses. He stayed with the 345th "Devil Hawks" and flew a Republic P-47 Thunderbolt until February 1945. On one occasion Gilormini led a squadron in an attack against Nazi positions in Conneto, Italy. During the attack his P-47 was struck by enemy anti-aircraft fire. Gilormini made a nose dive which put out the flames consuming his aircraft and rejoined his squadron. His squadron destroyed a strategic railroad and vehicles which were transporting military equipment.