Thunderbirds was originally conceived as a half-hour show. Nine episodes had already been shot and ten more written by the time ATV boss Lew Grade saw the pilot. He instantly decreed that each of the episodes should be one hour, not thirty minutes long, which represented both an opportunity and a challenge for Gerry and Sylvia Anderson’s AP Films. Scripts had to be extended, models rebuilt, and more footage shot. Ironically, when the series aired in the US, they were broken back down into half-hour lengths again.

The order Thunderbirds originally aired in was not the same as the order the episodes were produced in, which has often caused confusion, most recently because the various regional editions of the DVDs have sometimes been arranged in one order, sometimes another. One interesting continuity conundrum remains equally puzzling in either order: Grandma Tracy, although referred to as being already present on Tracy Island by Jeff in “Sun Probe” (episode 4 in order of production, episode 11 in order of original airing) isn’t actually shown to move there until “Move – And You’re Dead” (episode 9 in order of production, episode 20 in order of original airing).

Episodes are listed below in production order, along with the original airdate and order of screening.