Considering that the organisation is called 'International Rescue', what was the reason that Mr Anderson (RIP) chose the name 'Thunderbirds' for the craft? Obviously the name 'Thunderbird 1' is much more interesting than 'Rescue machine 1', however I am interested in exactly why the name 'Thunderbirds' was chosen.
According to 'The Complete Book of Thunderbirds 40th Anniversary Edition', Thunderbirds was originally based on the idea of a rescue organisation. In the early stages, the machines were simply called 'Rescue 1, 2, 3' etc. This was in keeping with the name of the show then, which was 'International Rescue'.
Apparently when they were early during the pre-production stages they were informed that they would need to change the name of the show and the craft. Searching for a name, Anderson thought about his brother (emphasis mine):
During the Second World War, Anderson's older brother, Lionel, had trained as an RAF pilot in Misa, Arizona, learning to fly at Falcon Field. Anderson recalled his brother telling him that a neighbouring field being used by the USAF was called Thunderbird Field. The name excited him and remained in the back of his mind for over twenty years, until he realised that Thunderbird was the perfect name for the International Rescue vehicles. It also made a 'punchier' title for the series and so 'International Rescue' became 'Thunderbirds'.