In February 1943, Perdomo entered an Army Air Forces (AAF) Pilot School in Chandler, Arizona. The AAF schools were civilian flying schools, under government contract, which provided a considerable part of the flying training effort undertaken during WWII by the Army Air Forces. Perdomo received his "wings" on January 7, 1944. He was then sent to the Army Air Forces Basic Flight School at Chico, California, where he underwent further training as a Republic P-47 Thunderbolt pilot. Upon the completion of his training he was assigned to the 464th Fighter Squadron which was part of the 507th Fighter Group that was sent overseas to the Pacific theater to the Island of Ie Shima off the west coast of Okinawa. The primary mission of the 507th was to provide fighter cover to 8th Air Force Boeing B-29's which were to be stationed on Okinawa.
The 507th began operations on July 1, 1945. Perdomo was assigned P-47N-2-RE number 146 aircraft (serial number 44-88211), maintained by crew chief S/Sgt. F. W. Pozieky. Perdomo nicknamed his airplane Lil Meaties Meat Chopper with the nose art depicting a diapered baby chomping a cigar in his mouth and derby hat on his head, clutching a rifle. The name referred to his first son, Kenneth, then a year and a half old. Perdomo flew his first combat mission on July 2, while escorting a B-29 to Kyushu.
Perdomo was a first lieutenant and a veteran of ten combat missions when on August 9, 1945 the United States dropped the world's second atomic bomb on Nagasaki, Japan. The allies were still awaiting Japan’s response to the demand to surrender and the war continued, when on August 13, 1945 1st Lt. Perdomo, shot down four Nakajima “Oscar” fighters and one Yokosuka “Willow” Type 93 biplane trainer. This action took place near Keijo/Seoul, Korea when 38 Thunderbolts of the 507th Fighter Wing, USAAF, encountered approximately 50 enemy aircraft. It was Perdomo's last combat mission, and the five confirmed victories made him an “Ace in a Day” and thus the distinction of being the last “Ace” of the United States in World War II. He was awarded the Distinguished Service Cross and the Air Medal with one leaf cluster.