A review of the Odyssey IIb autonomous underwater vehicle shows that energy costs associated with vehicle controls can be reduced and operational flexibility improved with relatively simple, low cost improvements. Because the operating speed that minimizes forward drag is not necessarily the same as that required for optimum sensor performance, a variable speed capability extending to the bottom of the vehicle speed range is sought. Optimizing Odyssey IIb AUV performance for slower speed operations and extended duration missions necessitates a multi-disciplinary review including control system design, hydrodynamic performance and sensor selection and utilization. Reducing the vehicle controls-fixed directional instability by adding vertical fixed fins, implementing an actuation filter, and designing a model based adaptive sliding controller improves the variable speed performance and reduces the control actuation necessary to provide the desired performance level with energy savings.