Efficient dynamic simulation of an underwater vehicle with a robotic manipulator. In this paper, an efficient dynamic simulation algorithm is developed for an underwater robotic vehicle (URV) with a manipulator. It is based on previous work on efficient O(N) algorithms, where N is the number of links in the manipulator, and has been extended to include the effects of a mobile base (the URV body). In addition, the various hydrodynamic forces exerted on these systems in underwater environments are also incorporated into the simulation. The effects modeled in this work are added mass, viscous drag, fluid acceleration, and buoyancy forces. With efficient implementation of the resulting algorithm, the amount of computation with inclusion of the hydrodynamics is almost double that of the original algorithm for a six degree-of-freedom land-based manipulator with a mobile base. Nevertheless, the amount of computation still only grows linearly with the number of degrees of freedom in the manipulator