US President-elect Donald Trump has named Gen James Mattis, a former marine who served in Iraq and Afghanistan, as his Defence Secretary. <br/> <br/>Gen Mattis, who is known as "Mad Dog", was an outspoken critic of the Obama administration's Middle East policy, particularly on Iran. <br/><br/>He has referred to Iran as the single most enduring threat to stability and peace in the Middle East. Mr Trump made the announcement in a speech in Ohio. <br/><br/>