In 1949, Oppenheimer knew the Soviets were getting close to the atomic bomb, so he had military aircraft in Japan daily sample the winds blowing east from Russia.
As a result, the US knew of the first Russian nuke test before it was publicly announced by them a few days later.
It took longer to get “earthquake” tremor recordings accurate enough, and “calibrated” to the shallow earth burials used for nuke testing, to begin believing the seismology records.
High altitude air sampling WAS a big deal back then, and those thousands of balloons every year were a large part of the secrecy whose inbreeding started the UFO reports.