I'd like to offer the following chord sequence. I got it from "The Folksingers Wordbook", and to my ear it's a better fit to the tune than the one previously listed.
Em Em G GWith your guns and drums and drums and guns, harroo, haroo
Em Em G B7With your guns and drums and drums and guns, harroo, harroo
Em Am Em B7With your guns and drums and drums and guns, the enemy nearly slew yaEm Am Em B7 Em Am EmMy darling dear you look so queer, Johnny I hardly knew ya