Autonomous underwater vehicles (AUVs) have shown great promise in fulfilling surveillance, scavenging, and monitoring tasks. Traditional gliders and streamlined AUVs are designed for long-term operational efficiency in expansive environments but are limited in cluttered spaces due to their shape and control authority; agile AUVs can penetrate cluttered or sensitive environments but are limited in operational endurance at large spatial scales. This paper presents the dynamic modeling and control design of an underwater hull capable of actuating its shape morphology. The prototype hull incorporates flexible, buckled fiberglass ribs to ensure a rigid shape that is actuated by modulating the length of the body’s semi-major axis. We represent the vehicle shape using a single control input actuating the vehicle’s length-to-diameter ratio. Hydrodynamic modeling of the flexible hull suggests that dynamic shape actuation can modulate the mass and drag properties of the hull to improve control of the vehicle’s forward speed. Using tools from nonlinear control theory, this paper presents the derivation of a shape-actuating autonomous control algorithm regulating the vehicle speed to a time-varying reference speed, subject to the actuator limits. The theoretical control results are illustrated using numerical simulations of the vehicle model.