Abstract : Recapitalization of the KC-135 aerial refueling tanker is very important for U.S. national security and has a significant impact on the U.S. national budget. Aerial refueling tankers are a critical part of U.S. military and national security strategy. Without them, air power cannot be deployed to overseas theaters in a timely way; it cannot be operated at militarily required distances from overseas bases; U.S.-based strategic air forces cannot execute overseas missions; and homeland defense air patrols would lose substantial effectiveness. The KC-135 constitutes the bulk of the current tanker force, embodying about 80 percent of U.S. aerial refueling capability. The KC-135 fleet is nearing 50 years of age, and it has exhibited some technical difficulties and increased costs of operation. KC-135 recapitalization also has major budgetary implications. The total cost of both operating the KC-135s until they are retired and acquiring and operating their replacements is in the $200 billion range over the next half century. This Analysis of Alternatives (AoA) addressed the cost-effectiveness of a wide range of alternatives for KC-135 recapitalization, including a large number of replacement systems and replacement schedules. In this AoA, the most cost-effective alternative means precisely the alternative whose effectiveness meets the military aerial refueling requirement at the lowest cost. The AoA primarily used requirements from the Defense Department's Mobility Capabilities Study, which was completed in 2005.