On 26 August 1967, Major Day was flying F-100F-15-NA, AF Serial No. 56-3954, call sign Misty 01, on his 26th Fast FAC sortie, directing a flight of F-105 Thunderchiefs in an air strike against a surface-to-air missile (SAM) site north of Thon Cam Son and west of Đồng Hới, north of the DMZ in North Vietnam. Day was on his 65th mission into North Vietnam and acting as check pilot for Captain Corwin M. "Kipp" Kippenhan, who was upgrading to aircraft commander. 37 mm antiaircraft fire crippled the aircraft, forcing the crew to eject. In the ejection, Day's right arm was broken in three places when he struck the side of the cockpit, and he also received eye and back injuries.