|The British naval cat rule|
Until 1975, the British navy required all its vessels to have a cat on board. As noted elsewhere in this book, cats were “working pets” on ships, their main purpose being to keep down the rodent population. But humans are human, and naturally they got attached to their four-legged friends.
Many sailors believed that cats were the guardian spirits of their ships, and that as long as a cat was on board, the ship was safe. If the cat happened to fall overboard and drown, the ship (so the superstition went) was doomed.