Seabird is one the yachts owned by Lady Penelope Creighton-Ward in the TV 21 Comics.
Seabird was first seen in the TV Century 21 Comic Mr Steelman in parts 7 to 8. Lady Penelope had it hidden in a cliff face somewhere in Britain off the coast. In order to get to it, the cliff face would slide back and Seabird would come out. However, whilst travelling to save fellow agent Roger Lyon, Seadbird was blown up by a missile.
Even though never speculated that she had the boat remade, Seabird has reappeared in other stories, which are set after Mr Steelman. In the audio adventure Introducing Thunderbirds Lady Penelope and Parker use a yacht to travel to Tracy Island. The yacht is never referred to as FAB 2, and so is presumed another Seabird.
In the Kevin McGarry book Lady Penelope: Cool For Danger Seabird is also used in the story, despite being called Mark I. It would make one more appearance time in John Theydon's Lady Penelope: The Albanian Affair however this time called George.
Seabird is 40-foot (12 m) and looks like an ocean-going cruiser. It can hold FAB 1 in a bomb proof garage.