The objectives of this program were the design and development of a high-efficiency, 1 megawatt, air-cooled, tunable pulsed klystron. The design was based on extensive use of a number of computer programs for all portions of the tube. Recent theoretical large-signal klystron work indicates state-of-the-art in efficiency at microperveance-2 operation could be extended by optimizing the beam behavior, the intercavity drift lengths, the cavity tunings, and the output coupling. Efficiency improvement results from the removal of electrons from the interbunch region and the optimization of their phase relationship at the outFut gap. The computer-predicted results indicated a conversion efficiency of 60% using the chosen beam and cavity parameters.