After graduating from TPS in June 1992, he worked as a TA-4J and EA-6B test pilot in Flight Systems Department of Strike Aircraft Test Directorate at NAS Patuxent River, Maryland. He was responsible for the management and conduct of a wide variety of projects, ranging from airframe fatigue life studies to numerous avionics upgrades. His primary efforts, however, were dedicated to flight test of the Advanced Capability (ADVCAP) EA-6B. Following his Patuxent River tour, McCool returned to Whidbey Island, and was assigned to Tactical Electronic Warfare Squadron 132 (VAQ-132) aboard the carrier USS Enterprise. He served as Administrative and Operations Officer with the squadron through their work-up cycle, receiving notice of his NASA selection while embarked on Enterprise for her final pre-deployment at sea period.