I'm watching the miniseries Anzacs, and in Episode 3, a few of the platoon try to convince a soldier to rejoin them after deserting, and he's taken up with a heavily armed group deserters who have organized some distance behind the lines (though close enough to hear the guns) on an old battlefield. Were these groups something that actually occurred? If so, how common?

It seems unlikely to me, but I figured I might as well ask.

Thank you.