It was a rare case of a Gerry Anderson production premiering in the US before it bowed in the UK.
The Day After Tomorrow made its debut as an episode of NBC's after-school anthology series, Special Treat, in December 1975, then aired in the UK on BBC 11 months later. Nick Tate (Space: 1999) and Brian Blessed star, with Ed Bishop (ex-UFO) narrating:
Insofar as I know, this has not been rerun in the US in recent memory.
Rating: None. Didn't see it the first time.