UK uses a sightly shorter mile than what I (western European SI unit user) uses when on water, and that was quite confusing the first time I tried to convert miles/hour to km/hours. Not a huge difference, but noticeable.
You're talking of the nautical mile. It's used globally in the marine industry. The nm is 1.1miles or 1.85km. And it's based on 1 arcminute of the circumference of the Earth.
