The huge capacity of the 747 made it an ideal airframe for the Advanced Airborne Command Post (E-4). Its first flight was on June 19, 1973, and its mission was to provide safe airborne headquarters for military and civilian leaders in times of national emergency. Hardness features protected the crew and their equipment from electromagnetic radiation and the effects of a nuclear blast. Designed for missions up to 72 hours in length, the E-4 included sophisticated communications equipment with a steerable dish antenna in a distinctive housing on top of the fuselage.