 The others were retired from 1972 to 1974 and placed in storage., three WB-57Fs are the only B-57 aircraft model still flying, in service with NASA.The RB-57F was the result of an Air Force "Big Safari" requirement for a high-altitude reconnaissance platform with better performance than the existing and similar RB-57D, some of which had been grounded as a result of wing spar failures.