The history of the 45th Fighter Squadron goes back to 22 November 1940, when the War Department constituted the 45th Pursuit Squadron (fighter). The unit was activated at Wheeler Field, Hawaii on 1 December 1940, where they served as part of the 15th Pursuit Group in defense of Hawaii. In January 1945, the 45th FS was ordered into combat, along with the other assigned squadrons in the 15th FG. They left Hawaii for Saipan in the Marianas Islands, staying there until the Marines on Iwo Jima could secure a landing strip.