  This paper addresses the problem of guidance and control of underwater
vehicles. A multi-level control strategy is used to determine (1) outer-loop
path-following commands and (2) inner-loop actuation commands. Specifically, a
line-of-sight path-following algorithm is used to guide the vehicle along a
three-dimensional path, and an $\mathcal{L}_1$ adaptive control algorithm is
used to determine the low-level rudder commands to accomplish path following.
The performance bounds of these outer- and inner-loop control algorithms are
presented. Numerical results obtained using a physics-based Simulink model are
used to aid in visualization of the control algorithm's performance.
