Complex sentence: Operation Argus was a series of nuclear weapons tests and missile tests secretly conducted during August and September 1958 over the South Atlantic Ocean by the United States's Defense Nuclear Agency, in conjunction with the Explorer 4 space mission.
Split into simpler sentences: Operation Argus was a series of United States nuclear weapons tests and missile tests secretly conducted during August and September 1958 over the South Atlantic Ocean. They were performed by the Defense Nuclear Agency, in conjunction with the Explorer 4 space mission.