Underwater walking machines offer a potential for replacement of human divers in certain aspects of underwater construction and inspection. One such vehicle, Aquarobot, is currently under test in Japan. However, this vehicle is currently too slow to be economically utilized, and limited hardware availability restricts progress in control software improvements. A software dynamic simulation model is desirable to relieve this restricted access. The problem addressed by this research is the modeling of system dynamics of underwater walking vehicles with sufficient simplification to achieve a real- time simulation. The approach taken includes an object-oriented, massless leg robot dynamic model and employs a high performance graphics rendering toolkit. The resulting simulations of a robotic joint actuator and of the robot itself, utilizing springs and dampers in the joints, runs in real-time. The robot simulation model executes on a four-processor machine with under fifteen percent utilization of the processor dedicated to system dynamics. This result indicates that the simulation is likely to retain real-time capability after replacing the springs and dampers with the more accurate joint actuator model also developed in this thesis.