Excalibur

Excalibur was the sword of King Arthur of England. When he fell in battle, Merlin placed it and his body in a dimension-crossing spaceship and hid it at the bottom of Lake Vortigern. In the late 20th century, the Doctor and Ace discovered Arthur's spaceship and retrieved Excalibur. (DW: Battlefield)

It is also one of the names sugested by Captain John Hart when he suggests a name used for Torchwood cradiff.