The USAF Fighter Weapons School at Nellis Air Force Base was the Air Force's premier institution for advanced fighter tactics training — the equivalent of the Navy's TOPGUN. Boyd served as an instructor at the FWS in the mid-1950s, where he earned his "Forty-Second Boyd" reputation. More importantly, the FWS was where Boyd developed the Aerial Attack Study (1960), the first systematic codification of air-to-air combat tactics. The environment of constant practice dogfighting gave Boyd the concrete empirical foundation that he would spend his career abstracting into increasingly general theories. The FWS represented the "deep immersion in concrete experience" that characterized the first phase of Boyd's intellectual evolution.