In 1943, Marion Magruder was deployed to England for a three-month stint to learn as much as possible about Radar Intercept Night Fighting from the RAF. Magruder was assigned to develop the U.S. Naval Radar Intercept Doctrine which entailed extensive modification of the British system into an almost totally different operational syllabus.

In October 1943, Magruder became the CO of the newly formed VMF (N)-533, which eventually took the nickname "Black Mac's Killers." The squadron deployed to Enewetak Atoll on May 6, 1944, to take over the night defense of the area. On November 30, 1944 "Black Mac's Killers" moved its base of operations from Enewetak to Engebi. On May 7, 1945, VMF (N)-533, with three day's™ notice, was ordered to deploy to Yontan Airfield on Okinawa to shore up sagging night defenses during the Battle of Okinawa.

They departed on the longest over-water flight of single-engine fighters in World War II.  Black Mac's Killers registered 35 enemy aircraft victories and one probable All-Radar-Intercepts, which was almost as many aircraft destroyed as the other night fighter squadrons on Okinawa, combined. VMF (N)-533 was the top-scoring Night Fighter Squadron of the Pacific Theater in World War II. In 15 months of overseas deployments, the "Killers" logged over 11,000 flight hours. For this action, the squadron was awarded the Presidential Unit Citation.