Another example is the recent cancellation of the F-108, a long range interceptor with a speed three times as great as the speed of sound, which was designed for use against manned bombers in the period of the mid 1960's. The substantial progress being made in ballistic missile technology is rapidly shifting the main threat from manned bombers to missiles. Considering the high cost of the F-108 system -- over $4 billion for the force that had been planned -- and the time period in which it would become operational, it was decided to stop further work on the project. Meanwhile, other air defense forces are being made effective, as described later in this message.

The size and scope of other important programs have been reduced from earlier plans. Notable in this category are the Jupiter and Thor intermediate range ballistic missiles, which have been successfully developed, produced, and deployed, but the relative importance of which has diminished with the increasing availability of the Atlas intercontinental ballistic missile.

The impact of technological factors is also illustrated by the history of the high energy fuel program. This project was started at a time when there was a critical need for a high energy fuel to provide an extra margin of range for high performance aircraft, particularly our heavy bombers. Continuing technical problems involved in the use of this fuel, coupled with significant improvements in aircraft range through other means, have now raised serious questions about the value of the high energy fuel program. As a result, the scope of this project has been sharply curtailed.