Spanish Ladies is a traditional English sea shanty of unknown origin. The first records of this song date from a ship's log of 1796. There have been a variety of different versions, some mentioning different distances between Ushant and Scilly, or different depths of the Channel.
Peter Duck suggests that the song must have described a homeward voyage beating up the Channel (PD36), but other versions not quoted in the book have the sailors running up the Channel with a following wind.
A recorded variation, by John Tams (part of a piece called Spanish Bride), had the setting being English soldiers leaving Spanish loved ones ashore as they left the Iberian peninsula in the Napoleonic Wars.
Further information and lyrics from Wikipedia.