Thunderbird Four is the specialist underwater vehicle used by International Rescue.
It is capable of 160 Knots submerged and 40 knots on the surface. Thunderbird Four is piloted by Gordon Tracy and is normally carried to the scene in Pod 4 aboard Thunderbird Two.
All the Thunderbirds were designed by Brains, the technical genius behind International Rescue.
The series was designed by Gerry and Sylvia Anderson and first broadcast in the UK in 1966.