US Marines battling the Taliban in southern Afghanistan have had to call in helicopter gunships for support, as a major offensive enters its fifth day today. <br/><br/>The marines have faced sustained and heavy machine-gun fire from fighters hiding in bunkers, as they try to gain control of the Taliban haven of Marjah. <br/><br/>Some 15,000 troops are taking part in the joint NATO and Afghan operation. To the north, British forces have discovered an insurgent cache of stolen Afghan army and police uniforms. The find suggests the Taliban could have been planning attacks disguised as Afghan security personnel.<br/>