REVGEN provides a computerized ocean acoustic environment for the development of a modern active sonar system. [D, W. Princehouse, “Real‐time reverberation generator,” J. Acoust. Soc. Am.57, S68(A) (1975).] During an exercise, it is important that it run in as near to real time as possible. We have developed a method whereby the numerically difficult and time‐consuming portion of ray tracing can be performed before the exercise starts, and the results used rapidly when needed. We work in the limit of geometrical acoustics and assume that the sound velocity profile depends only on depth, not range or time. While many ray‐tracing techniques can be adapted, we have used those of NISSM II. [Henry Weinberg, Naval Underwater Systems Center, New London, CT 06320. NUSC Technical Report 4527.]A function of two variables is defined, range versus launch depth and vertex velocity. Knowledge of this function allows ray tracing to be performed. This function may be computed prior to its need, a lengthy process. By encoding it in an efficient fashion, however, it may be stored in computer memory for rapid access when needed. Examples of ray tracing, caustic detection, and multipath propagation will be shown.