Just to reiterate, a 50 gun ship with 500 men is unlikely. A Royal Navy ship of 50 guns had an established crew of 350. A 50gun privateer would be about the largest privateer ever recorded. Also I cannot find any action in the Seven Years War or the War of the Austrian Succession that the song could relate to. The ship names apart from Dreadnought are unknown.

So it seems it's just a fantasy. But there's nothing wrong with that.