It was 1941 and the war was not going well for the Allies. The Nazis were advancing on multiple fronts, including deep into the unprepared Soviet Union. Britain was now locked into an uneasy but necessary friendship with that Communist power.
HMS Trident, a Royal Navy submarine, docked at Polyarny on the Arctic Ocean coast of the Soviet Union. While his boat was undergoing repairs, Commander Geoffrey Sladen dines with the Soviet post admiral. He comments that his wife sometimes struggled to push their infant's stroller through snow. The Admiral suggests having a reindeer pull the stroller and promptly has a reindeer delivered to Trident as a gift to Commander Sladen's wife.
This was a diplomatically uneasy time, so Commander Sladen knew that it would be unwise to refuse the gift, even though transporting a reindeer by submarine back to Britain would be difficult. The crew names the reindeer Polyanna after the port and takes on a barrel of moss for her to eat during the voyage back home.
On the way to Britain, Trident recieves new orders: stay on patrol in the area on the hunt for German warships. The supply of moss runs out, so Polyanna eats condensed milk instead. She hangs out in the torpedo room and sleeps beneath the captain's rack. But she is not exactly toilet trained and gets rather stinky. Submarines are called "pigboats" for a reason, but Trident gets unusually smelly due to Polyanna's contributions.
Despite spending six weeks on a submarine, Polyanna arrives in the UK healthy and has, in fact, gained weight, making removing her from the boat an added challenge. She lives for five more years at a the Regents Park Zoo in London.
-via Nag on the Lake