The HMS Seaspite was a Royal Naval Base located on Fortress Island. It was commanded by Captain John Hart, who was assisted by Third Officer Jane Blythe.
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The ships dock. (DW: The Sea Devils)
The Third Doctor and Jo Grant visited Seaspite during the Sea Devil Crisis. The base came under attack by the Sea Devils living under an abandoned sea-fort close to the Island but the Naval Officers fought them off with the help of the Doctor. SONAR was used aboard the ship. (DW: The Sea Devils)