The Ship's Cat by Richard Adams

The ship's cat is introduced as a patriotic swashbuckling crew member of the English privateer Alcestis. After attacking a lone Spanish ship, the Alcestis is defeated by Spanish reinforcements and its crew taken as captives to the Panamanian port of Chagres.

The ship's cat is initially imprisoned, but the gaoler's daughter takes pity on him and has him released to serve in the gaoler's kitchen. After the gaoler and his companions become drunk celebrating Saint Philip's Day, the ship's cat steals the keys to the gaol and releases his shipmates.

Together, they steal a ship from the harbor and sail for home, pursued by their erstwhile captors. Their pursuers are frightened off by the sudden appearance of Sir Francis Drake (outward bound on his global circumnavigation of 1577).

After Drake departs, the ship's cat reveals that he has discovered a hoard of treasure in the ship's hold. The crew sail home to England, where they are greeted as heroes and the cat is knighted by Queen Elizabeth I.