 On 25 June 1967, with extensive previous service flying two tours in F-100s, Major Day was made the first commander of Detachment 1, 416th Tactical Fighter Squadron, 37th Tactical Fighter Wing based at Phu Cat Air Base.Under the project name "Commando Sabre", twin-seat USAF F-100Fs were evaluated as a Fast Forward Air Controller (Fast FAC) aircraft in high threat areas, given that F-4 Phantom II aircraft were in high demand for strike and Combat Air Patrol (CAP) roles.Using the call sign "Misty", the name of Day's favorite song, his detachment of four two-seat F-100Fs and 16 pilots became pioneer "Fast FACs") over Laos and North Vietnam.