In this paper, we developed a Manta-type AUV (Autonomous Underwater Vehicle) and analyzed its control performance as well as its dynamic characteristics underwater. The nonlinear motion of equations, which are expressed in terms of hydrodynamic coefficients obtained by various experiments, are used to simulate the motion of a Manta AUV underwater. We applied the sliding-mode theory to control the heading angle and depth of the vehicle, and confirmed the effectiveness of the control algorithm through simulations and sea-trials.