relaxed as the second ceasefire took effect. Wilson's return to power in 1974 helped to return Anglo-American relations to normality. On July 23, 1977, officials from the United Kingdom and the United States renegotiated the previous Bermuda I Agreement, and signed the Bermuda II Agreement under which only four airlines, two from the United Kingdom and two from the United States, were allowed to operate flights between London Heathrow Airport and specified "gateway cities" in the United States. The Bermuda II Agreement was in effect for nearly 30 years until it was eventually replaced by the EU-US Open Skies Agreement, which was signed on April 30, 2007, and entered into effect on March 30, 2008. 1980s Margaret Thatcher (Prime Minister, 1979–1990) and Ronald Reagan (President, 1981–1989) bonded quickly. According to David Cannadine: In many ways they were very different figures: he was sunny, genial, charming, relaxed, upbeat, and with little intellectual curiosity or command of policy detail; she was domineering, belligerent, confrontational, tireless, hyperactive, and with an unrivalled command of facts and figures. But the chemistry between them worked. Reagan had been grateful for her interest in him at a time when the British establishment refused to take him seriously; she agreed with him about the importance of creating wealth, cutting taxes, and building up stronger defences against Soviet Russia; and both believed in liberty and free-market freedom, and in the need to outface what Reagan would later call 'the evil empire'. Throughout the 1980s, Thatcher was strongly supportive of Reagan's unwavering stance towards the Soviet Union. Often described as "political soulmates" and a high point in the "Special Relationship", Reagan and Thatcher met many times throughout their political careers, speaking in concert when confronting Soviet general secretary Mikhail Gorbachev. During the Soviet–Afghan War, Britain was covertly involved and helped support the US military and financial aid to the anti communist mujaheddin insurgents in Operation Cyclone. In 1982, the British Government made a request to the United States, which the Americans agreed upon in principle, to sell the Trident II D5 ballistic missile, associated equipment, and related system support for use on four nuclear submarines in the Royal Navy. The Trident II D5 ballistic missile replaced the United Kingdom's previous use of the UGM-27 Polaris ballistic missile, beginning in the mid-1990s. In the Falklands War in 1982, the United States initially tried to mediate between the United Kingdom and Argentina,