During her first year as prime minister she supported NATO's decision to deploy US nuclear cruise and Pershing II missiles in Western Europe, permitting the US to station more than 160 cruise missiles at RAF Greenham Common, starting in November 1983 and triggering mass protests by the Campaign for Nuclear Disarmament. She bought the Trident nuclear missile submarine system from the US to replace Polaris, tripling the UK's nuclear forces at an eventual cost of more than £12 billion (at 1996–97 prices). Thatcher's preference for defence ties with the US was demonstrated in the Westland affair of 1985–86, when she acted with colleagues to allow the struggling helicopter manufacturer Westland to refuse a takeover offer from the Italian firm Agusta in favour of the management's preferred option, a link with Sikorsky Aircraft. Defence Secretary Michael Heseltine, who had supported the Agusta deal, resigned from the government in protest.