The development of a line of planetary drives having characteristics suitable for use in hydrostatically driven track vehicles features compact design, simple installation, full load output bearings. Highly reliable, efficient performance is assured by thorough dynamometer and field tests. Propel performance can be predicted on a load/life basis for each specific application. Design logic for the selection of planetary gearing is reviewed and other design features are discussed. The importance of testing for rating confirmation is stressed.THE PURPOSE of this paper is to highlight what has proven to be a successful approach to the design, testing and application of planetary gear speed reducers for hydrostatic crawler propel systems. The design concepts embody application of high speed low torque hydraulic motors to low speed high torque output requirements.