ample time to guide intercept aircraft onto the target as it moved across the display. This led to low blip/scan ratios and inaccurate prediction of aircraft trajectories. This had been compounded by the difficulty of quickly scrambling intercept aircraft. Missiles solved both of these problems. Missiles stations guided their missiles with their own radar systems, which had maximum ranges only slightly longer than the missile's own flight range, about 40 km in the case of the SA-2 Guideline; therefore they had much higher PRFs, and as a result the blip/scan problems were greatly reduced. Defenders would still have the problem of finding the target in time to prepare for a missile counterattack, but this was by no means as difficult or as time consuming as scrambling manned aircraft and relying on the radar operator to guide them onto the target before the aircraft left radar range. By the time the A-12 was operational in the early 1960s the blip/scan avoidance technique was no longer considered useful. The A-12 never flew over the Soviet Union (although it came close to doing so) and was limited to missions against other countries, like Vietnam. Even here the performance of the aircraft proved questionable, and A-12s were attacked by SA-2 missiles on several occasions, receiving minor damage in one case. References The U-2's Intended Successor:Project Oxcart, 1956-1968 Radartutorial Thomas McIninch, "The Oxcart Story" , Studies in Intelligence 15 (Winter 1971), Released 1994. Retrieved: 10 July 2009. Gregory Pedlow and Donald Welzenbach, The Central Intelligence Agency and Overhead Reconnaissance: The U-2 and OXCART Programs, 1954 - 1974, Chapter 6, "The U-2's Intended Successor:Project Oxcart, 1956-1968". Washington, DC: Central Intelligence Agency, 1992. Retrieved: 2 April 2009. Further reading Queen, F. D.; Maine, E. E., Jr., A blip-scan ratio scoring system, 1974, Naval Research Lab, Washington, DC. Radar