'Triple masted. Double decks. Fifty guns. Isn't she a beauty?' - Tintin on the Unicorn.
The Unicorn was the ship captained by Sir Francis Haddock, sailing in the service of King Louis XIV of France. Even with its fifty guns on two decks and three masts the ship was boarded and taken over by pirates under the command of Red Rackham.
When it became clear that his ship was sinking, after taking heavy cannon fire from the Unicorn, Red Rackham began to transfer his loot to the Unicorn. After escaping from imprisonment on the ship, Haddock managed to kill Rackham and destroy the ship with the pirate crew on board. There were three models of this ship made by Sir Francis for his three sons which contained scrolls that when lined up together reveal the coordinates of the location of the sunken Unicorn.
The Unicorn is likely based on the historical ship Unicorn (1634) which was historically commanded by Captain Richard Haddock, grandfather of the more famous Sir Richard Haddock. Under the elder Haddock, she served Charles I in the English Royal Navy, and later under Oliver Cromwell in the Commonwealth Navy.