- You may be looking for the Earth sea vessel.
The Fortitude was a sailing vessel on Hydra. It was the head of a flotilla.
When the TARDIS landed on the cargo ship Hopeful, the First Doctor, Ian, Barbara and Susan were discovered by the crew and taken to the Fortitude. The ship was attacked and sunk by the Voord with the Doctor and Barbara still on board. They managed to survive, but were captured by the Voord. (AUDIO: Domain of the Voord)