By early 1989, the operational lifetime of the F-4 Phantom was ending, and the number of RF-4C squadrons serving both on active-duty as well as in Air National Guard units was being reduced. In large part, the RF-4C was being replaced by the ability of the Lockheed U-2 TR-1A and TR-1B, which had taken over the tactical reconnaissance mission. The collapse of the Soviet Union and the dissolution of the Warsaw Pact led to accelerated retirement plans, and the retirement of the last of the RF-4Cs was in the planning stages when Iraq invaded Kuwait in August 1990, and further inactivation plans were put on hold. Consequently, the RF-4C was still in service with the USAF at the time of Operation Desert Shield.