In policy debates concerning large scale R&D efforts, the achievements of the Manhattan and Apollo projects are frequently cited as evidence of "Yankee ingenuity" and the ability to overcome technical obstacles. In this article, the factors which contributed to the success and failure of large scale "crash" development projects are analyzed systematically. Successes are distinguished from failures according to two criteria. First, while the successes are marked by "parallel" development of technological components which began only after the basic scientific and technical obstacles had been overcome and the basic feasibility had been demonstrated, in the failures, parallel development began much earlier. In addition, the successful "crash" projects, such as the atomic bomb effort and the moon program, were designed to meet static technical goals and did not depend on overcoming countermeasures. The unsuccessful projects, such as the Safeguard ballistic missile defense (BMD) system, failed in the face of changes in Soviet military technology. Using these criteria to analyze the Reagan administration's space-based ballistic missile defense program (SPBMD), the author concludes that despite the claims made by supporters, this R&D effort is not similar to the Manhattan or Apollo projects. Rather, like the Nuclear Airplane and Skybolt missile, parallel developments have begun prior to proof of feasibility, and like the Safeguard BMD, the SPBMD must adapt to countermeasures.