apparently it dates from the late 1800s and is a slang word for a fight or argument, I wonder if it referres to a foreign campaign maybe. Possibly Irish?
yes, have now looked it up in my slang dictionary and it says from the Irish name Barney, presumably because the Irish are supposed to get drunk and fight; first use seems to have been in Australia, however, where there were a lot of Irish immigrants. Gives the spelling as barney.