Mobile systems traveling through a complex environment present major difficulties in determining accurate dynamic models. Autonomous underwater vehicle motion in ocean conditions requires investigation of new control solutions that guarantee robustness against external parameter uncertainty. A diving-control design, based on Lyapunov theory and back-stepping techniques, is proposed and verified. Using adaptive and switching schemes, the control system is able to meet the required robustness. The results of the control system are theoretically proven and simulations are developed to demonstrate the performance of the solutions proposed.