sydney three hundred u.s. marines fly australia sunday troop rotation come end first 1,250-strong force leave pacific nation station six months country far north sixth rotational group advance contingent send since program begin former u.s. president barack obama agree send troop 2011 part military pivot asia-pacific region first time rotation include aviation combat section 13 aircraft include four mv-22 osprey tilt-rotor aircraft accord australia department defence australian u.s. troop also practice disaster relief humanitarian assistance combine force remote location first time rotational force station darwin state capital northern territory strategically locate coastal doorstep indonesia east timor papua new guinea six-month deployment u.s. troop participate 12 joint exercise australian defence force give opportunity interact range countries include china indonesia japan new zealand malaysia philippines singapore thailand vietnam australia alliance unite state important defense relationship remain central australia security captain bryan parker deputy commander australia northern command say statement presence u.s. marines across northern territory play vital role underwrite security stability across indo-pacific say add force posture initiatives essential preserve stability come decades marine rotation number originally expect reach 2,500 2017 far rise 1,250 accord abc news report hundreds u.s. marines leave australia troop rotation