This study is concerned primarily with the concluding phase of the program to develop a nuclear-propelled aircraft for manned flight. Covering the period from January 1959 to March 1961, it seeks to make clear the factors that brought about the termination of the program. The emphasis is on the policy-management level, and technological factors are dealt with only to the extent that they became involved at that level. A summary review is given of the earlier phase from 1946 through 1958. For this phase the study draws heavily, though by no means exclusively, from a historical study prepared by the Wright Air Development Center in 1959, The USAF Aircraft Nuclear Propulsion Program. Charts and tables are provided in an appendix to summarize the financial support of the program and to illustrate the organizational structure for its management. Nuclear Propulsion for Manned Aircraft is part of the larger History of Headquarters USAF, Fiscal Year 1960. It is being published separately to make it more readily available throughout the Air Force.