Well, it sounds to me like a folksong about the British Navy's impressment of sailors. Many sea powers, especially during the 18th and early 19th centuries (when large navies of huge sailing ships were prevalent)had a shortage of men. After all, life on a wooden ship at sea must have been far from pleasant, and the labor of an enlisted seaman was grueling (as you will know if you have ever sailed!).
So, many countries, Britain most notably, allowed their naval captains to form "press gangs" and draft citizens (usually of the lower class, for obvious reasons) into the navy. Needless to say, this was not popular.
As our American history experts will tell you, British impressment was cited as a cause of the War of 1812, at which time Americans (who also spoke English and were therefore indistinguishable from englishmen to officers) were sometimes forced aboard English vessels to help fight Napoleon.
As for the particulars of the song, I couldn't tell you much, but Ewan MacColl sings a rather nice version of it(as he does of practically everything else). Hope I was of some help!