Complex sentence: The first KB-50 flew in December 1955 and was accepted by the Air Force in January 1956, the tankers from then on steadily entering the operational inventory of the Tactical Air Command (TAC).
Split into simpler sentences: The first KB-50 flew in December 1955 and was accepted by the Air Force in January 1956. The tankers steadily entered the operational inventory of the Tactical Air Command (TAC).