A British children's television show from the 1960s, made with puppets on strings (the technique was called 'Supermarionation'). The story: a rich ex-astronaut and his five sons run a secret organization called International Rescue. When people are in terrible danger — trapped in a burning building, sinking in a submarine, falling out of the sky — the family flies out in amazing machines named Thunderbird 1, Thunderbird 2, and so on, and saves them. The famous line at the start of each episode is 'Thunderbirds are go!' — which is odd English, but that is exactly how it is said, and British people still say it as a joke when a group is finally ready to start something. The word is always plural here, and it takes a plural verb even though it is one programme: people say 'Thunderbirds was on TV' when they mean the show, but 'Thunderbirds are go' inside the show. Note that this is a name, so you will meet it mostly in conversations about old television, in British newspapers, or as a joke. Be careful: 'thunderbird' with a small letter is a different thing — a huge bird in the stories of some Native American peoples, whose wings make thunder — and the TV show borrowed its name from there.