Allan
Yes, I think you are right - but this one's inclusion of "Buttermilk Hill" links it more to the AWOI (It's in Pennsylvania). Actually, it makes me wonder why the name "Johnny" appears in a number of American military folk songs - certainly the American Colonials were referred to as "Johnathens" by the British Royal Navy in both the War of Independence and the 1812 war - and American privateers long before that.
But, then - perhaps it was just a common name!
Cheers
Graeme