Thunderbird 4 is International Rescue's rescue submarine. Piloted by aquanaut Gordon Tracy TB4 is usually carried to the rescue zone by TB2 in pod 4 which is dropped from low altitude into the water. TB4 then fires a battery of rocket tubes to power out of the pod and into the ocean, where the Turbo Drive propulsion system takes over. Port and starboard mounted jet engines provide propulsion for surface cruising.

TB4 is equipped with extensive underwater rescue equipment mounted in the nose of the craft behind the adjustable high powered lighting trough. The equipment includes a missile tube (commonly used for underwater demolition) and three hydraulic rams one of which carries interchangeable tool heads. A telescopic 'Autolock' provides an exit for Gordon when he has to leave the craft whilst underwater.

The pilots seating position provides a wide view of the area around the craft and this is further enhanced by the centrally mounted TV monitor which relays information back to him.