The F-4D was an improved “C” variant with most improvements being internal electronics and avionics. The F-4D entered operational service in April 1966 and joined the combat forces in Southeast Asia in May 1967. With the arrival of the “D” most of the “C” variant were reassigned to ground attack with the “D”s taking on the air-to-air interceptor role. In 1968 – 1969 a total of 825 “D” models were produced 793 for the USAF and 32 for the Iranian Air Force. Because of growing tension between North and South Korea the South Korean government placed an initial order for 18 F-4Ds. The USAF filled this order with aircraft that were already in stock rather than building brand new aircraft. The first aircraft of the 18 ordered arrived at Taegu AB on August 29, 1969. F-4D 64-0935 was transferred to the RoKAF in August 1969 assigned to the 11th TFW, 110th TFS. RoKAF eventually received somewhere between 70 and 92 ex-USAF F-4Ds.