I lapped this up eagerly when it was first syndicated in the US, I was in high school at the time. It wasn't until a few years later that I saw Doppelgänger, probably the first time it was on TV.

I was actually introduced to Gerry and Sylvia Anderson as a much younger kid, when I saw Fireball XL-5 on Saturday morning TV. But I missed Thunderbirds until I was an adult!