It was popular in the UK; it was shown there on ITV in the 1960s, with several repeat runs on BBC2 from 1983 onwards.
Despite its intentional Cold War overtones, the show also made it across the Iron Curtain into Hungary, where it was dubbed and aired under the title "Attack from an Alien Planet" (Hungarian: Támadás egy idegen bolygóról) between July 4 and September 5, 1980.