Just Nuisance - The Only Dog Ever Officially Enlisted in the Royal Navy

Just Nuisance in uniform

Just Nuisance (1 April 1937-1April 1944), a Great Dane of remarkable size and legendary appetite, was the only dog ever to be officially enlisted into the Royal Navy. He was beloved of sailors in the greater Cape Town, South Africa area.

He was enlisted on 25 August 1939. His surname was entered as "Nuisance" and, rather than leaving the forename blank, he was given the moniker "Just". His trade was listed as "Bonecrusher" and his religious affiliation as "Scrounger", although this was later altered to the more charitable "Canine Divinity League (Anti-Vivisection)". To allow him to receive rations and because of his longstanding unofficial service, he was promoted from Ordinary Seaman to Able Seaman.

Nuisance's service record was not exemplary. Aside from the offences of travelling on the trains without his free pass, being absent without leave, losing his collar and refusing to leave the pub at closing time, his record shows that he was sentenced to having all bones removed for seven days for sleeping in an improper place — to wit, the bed of one of the Petty Officers. He also fought with the mascots of ships that put in at Simon's Town, resulting in the deaths of at least two of them. 

The above quoted from the Wikipedia article on him.

From The History Guy