Abstract This paper is intended to set forth the latent possibilities in heavy-duty free-piston machinery. The cycle promises diesel efficiency from a simple low-temperature gas turbine having low first costs. Many features are described in the paper. Cooper-Bessemer has built a test plant and is now investigating its operating characteristics. No conclusions have been announced. Economic evaluations are being made requiring additional field work which includes an examination of the general acceptance by engineering and operating people who ultimately will decide the actual utility. Detailed cost studies of complete plants, including careful estimates of the machinery, have been made for electric power generation, pipe-line pumping, and marine installations. Some of these have been made available for use in this paper with the belief that such an evaluation of this prime mover will be of general interest to the Society.