While successful developments in aviation receive considerable attention, the projects that failed or otherwise did not live up to expectations receive far less, if any, scrutiny. Typically, unsuccessful efforts are briefer in duration and have a less visible paper trail. Thus, while the literature is rich in success stories, we tend to "forget" or simply bury our failures. And, as one observer has suggested, "that there were failures, mistakes, and wrong turns reminds us that progress is not inevitable, that acknowledged error can be as instructive as success, and that roads not taken impose a price all their own." Here, author Kenneth P. Werrell tells of a race to overcome obstacles - politics, resources, competing technologies, timing - in the quest to deliver quality, if not war-winning machinery. The focus of Air Force Disappointments, Mistakes, and 1940-1990 is on aircraft (e.g., bombers, fighters, transports) and missiles (e.g., cruise missiles, standoff missiles, ballistic missiles, surface-to-air missiles, air-to-air missiles). An intelligence system is also evaluated. These case studies give the context and details of the development, testing, and, as appropriate, operational service. Highlighting the problems and criticisms of these systems then provides an opportunity to determine what went wrong. The reasons for the failures of these systems vary from the obvious (money, delays, technical problems) to more complex reasons, such as the foe's reaction, politics, new technologies, and timing. The tale of these disappointments is a heretofore untold story. These projects, in which the US Air Force stumbled, are outliers within the overall success of the service, and, fortunately, its successes outnumber the failures.