Background: Chesley Sullenberger was born in Denison, Texas, His father was a descendant of Swiss-German immigrants named Sullenberger. He has one sister, Mary. The street on which he grew up in Denison was named after his mother's family. According to his sister, Sullenberger built model planes and aircraft carriers during his childhood, and says he became interested in flying after seeing military jets from an Air Force base near his house.
Context: Sullenberger was appointed to the United States Air Force Academy, entering with the Class of 1973 in June 1969. He was selected along with around a dozen other freshmen for a cadet glider program, and by the end of that year, he was an instructor pilot. In the year of his graduation, 1973, he received the Outstanding Cadet in Airmanship award, as the class "top flyer". Following graduation with a Bachelor of Science and his commissioning as an officer, the Air Force immediately sent Sullenberger to Purdue University to pursue a master's degree prior to entering Undergraduate Pilot Training (UPT).  Following completion of his graduate degree at Purdue, he was assigned to UPT at Columbus AFB, Mississippi, flying the T-37 Tweet and T-38 Talon. After earning his wings in 1975 as a USAF Pilot, he completed replacement training in the F-4 Phantom II at Luke AFB, Arizona. This was followed by his assignment to the 493d Tactical Fighter Squadron of 48th Tactical Fighter Wing at RAF Lakenheath, United Kingdom, where he flew as a United States Air Force fighter pilot in the F-4D Phantom II.  Following his assignment at RAF Lakenheath, he was reassigned to the 428th Tactical Fighter Squadron of the 474th Tactical Fighter Wing at Nellis AFB, Nevada, again flying the F-4D. He advanced to become a flight leader and a training officer, and attained the rank of captain, with experience in Europe, the Pacific, and at Nellis Air Force Base, as well as operating as Blue Force Mission Commander in Red Flag Exercises. While in the Air Force, he was a member of an aircraft accident investigation board.
Question: When did Chesley begin his military service?. Whats the answer?
June 1969.