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Underwater vehicle control is the discipline of designing guidance, navigation, and feedback-control systems that stabilize the motion and steer the trajectory of unmanned underwater vehicles, including remotely operated vehicles and autonomous underwater vehicles within a six-degree-of-freedom hydrodynamic environment. The control problem is defined by the nonlinear, coupled equations of rigid-body motion expressed in a body-fixed reference frame, with hydrodynamic forces from added mass, linear and quadratic damping, buoyancy, thrust from propellers or fins, and environmental disturbances from currents and waves ^[1]. Because underwater vehicles are typically underactuated—possessing fewer control inputs than degrees of freedom—the control architecture must handle nonholonomic constraints, coupling between surge and sway modes, and buoyancy-induced pitch and roll moments that depend on center-of-gravity relative to center-of-buoyancy separation. Controllers are synthesized using model-based methods such as sliding-mode control, feedback linearization, sliding mode observers for estimating unmeasured velocities, and Lyapunov-based stability proofs that account for parametric uncertainty in hydrodynamic coefficients ^[2]. The guidance layer generates desired trajectories using waypoint navigation, path-following algorithms that satisfy surge and heading references, and dynamic positioning strategies that hold position against current disturbance while maintaining depth and heading stability ^[3].