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The Boeing E-4 Advanced Airborne Command Post, with the project name "Nightwatch",〔.〕 is a strategic command and control military aircraft operated by the United States Air Force (USAF). The E-4 series was specially modified from the Boeing 747-200B. The E-4 serve as a survivable mobile command post for the National Command Authority, namely the President of the United States, the Secretary of Defense, and successors. The four E-4Bs are operated by the 1st Airborne Command and Control Squadron of the 55th Wing located at Offutt Air Force Base, near Omaha, Nebraska. An E-4B is denoted a "National Airborne Operations Center" when in action.〔.〕 ==Development== Two of the original 747-200 airframes were originally planned to be commercial airliners. When the airline did not complete the order, Boeing offered the airframes to the United States Air Force as part of a package leading to a replacement for the older EC-135J National Emergency Airborne Command Post (NEACP). Under the 481B NEACP program the Air Force Electronic Systems Division awarded Boeing a contract in February 1973 for two unequipped aircraft, designated E-4A, powered by four P&W JT9D engines, to which a third aircraft was added in July 1973. The first E-4A was completed at the Boeing plant outside Seattle, Washington in 1973. E-Systems won the contract to install interim equipment in these three aircraft, and the first completed E-4A was delivered to Andrews AFB, Maryland in December 1974. The next two were delivered in 1975, the third differed by being powered by the GE F103 engine, which was later made standard and retrofitted to the previous two aircraft. The "A" model effectively housed the same equipment as the EC-135, but offered more space and an ability to remain aloft longer than an EC-135.〔Michell 1994, p. 265.〕 In November 1973 it was reported that the program cost was estimated to total $548 million for seven 747s, six as operational command posts and one for research and development.〔 In December 1973 a fourth aircraft was ordered; it was fitted with more advanced equipment, resulting in the designation E-4B. On 21 December 1979 Boeing delivered the first E-4B (AF Serial Number 75-0125),〔 which was distinguished from the earlier version by the presence of a large streamlined radome on the dorsal surface directly behind the upper deck. This contains the aircraft's SHF satellite antenna.〔Bowers 1989, p. 528.〕 By January 1985 all three E-4As had been retrofitted to E-4B models.〔 The E-4B offered a vast increase in communications capability over the previous model and was considered to be 'hardened' against the effects of electromagnetic pulse (EMP) from a nuclear blast. Hardening the aircraft meant that all equipment and wiring on board was shielded from EMP. Additional steps were taken to block radiation from the aircraft's cabin air management system and cockpit, including the novel use of the same screens used to cover the windows of microwave ovens placed over the flight deck windows. The E-4B fleet has an estimated roll-out cost of approximately US$250 million each. In 2005 the Air Force awarded Boeing a five-year, US$2 billion contract for the continued upgrade of the E-4B fleet.〔(【引用サイトリンク】date= 21 December 2005 )〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Boeing E-4」の詳細全文を読む スポンサード リンク
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