A Hot Day in a Cold war. An RB-47 vs. Mig-17S, April 28, 1965‪.‬

Early in the Cold War, in 1946, the United States had begun conducting military reconnaissance flights near the borders of the Soviet Union and its satellites. These missions, known as "PARPRO"--for Peacetime Airborne Reconnaissance Program--were intended to obtain information on Soviet strategic military capabilities as well as to prevent the possibility of a surprise attack on the U.S. or its Western allies. Unlike the overflights of denied territory that U.S. aircraft conducted in later years, PARPRO sorties were entirely legal as they were not intended to penetrate Soviet or other potential belligerents' airspace. Whereas the overflights required Presidential approval, U.S. military theater commanders approved the more common PARPRO missions. In 1960, the shoot-down of Francis Gary Powers led the Eisenhower Administration to suspend the practice of penetrating Soviet or other potential belligerents' airspace. But PARPRO missions continued as they had since the 1940s. Regardless of intent, however, many PARPRO aircraft were attacked: some were downed; others, like the RB-47 in the following account, survived. Most PARPRO routes were used repeatedly and were known in the Strategic Air Command (SAC) as "library routes," a practice that tacitly communicated to potential belligerents that the mission was not of hostile intent. (1)