In 1968 the Air Weather Service's RB-57Fs were redesignated WB-57Fs, and they continued to be used in the atmospheric sampling role, mostly on behalf of the AEC. Some of the aircraft were fitted with probes to scoop up airborne particles in a program of ongoing monitoring of nuclear tests. Most of this activity was centered on the nuclear tests carried out in Communist China, but some of it was used in U.S. air space to monitor air in the aftermath of underground nuclear tests.