This paper illustrates a method of digitally simulating the motion and control of vehicles. This method of simulation has been used for the simulation of a large variety of systems, including a six-degree-of- freedom simulation of Gemini reentry with guidance and control, a six-degree-of-freedom aircraft simula tion, missile control simulations including bending modes, trajectory problems, and many others. The major advantage of the method, in addition to the speed of computation, is that a detailed an alysis of the system is carried out during the develop ment of the simulation. Although, for small problems, simulations using this method can be derived by hand, large simula tions generally require a computer program to com pute root locus points and z-transforms. © 1965, Sage Publications. All rights reserved.