McCool completed flight training in August 1986 and was assigned to Tactical Electronic Warfare Squadron 129 at Whidbey Island, Washington, for initial EA-6B Prowler training. His first operational tour was with Tactical Electronic Warfare Squadron 133, where he made two deployments aboard USS CORAL SEA (CV-43) to the Mediterranean Sea, and received designation as a wing qualified landing signal officer (LSO). In November 1989, he was selected for the Naval Postgraduate School/Test Pilot School (TPS) Cooperative Education Program. After graduating from TPS in June 1992, he worked as TA-4J and EA-6B test pilot in Flight Systems Department of Strike Aircraft Test Directorate at 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, Lieutenant Commander McCool returned to Whidbey Island, and was assigned to Tactical Electronic Warfare Squadron 132 aboard USS ENTERPRISE (CVN-65). He served as Administrative and Operations Officer with the squadron through their work-up cycle, receiving notice of NASA selection while embarked on ENTERPRISE for her final pre-deployment at-sea period.
McCool has over 2,100 hours flight experience in 24 aircraft and over 400 carrier arrestments.