Effective locomotion and maneuvering in aquatic environments is important for survival for marine fauna. The ability to move quickly, change direction, and tune energy consumption for long migrations is critical for escape from predators and pursuit of prey. This controlled propulsion in terms of varying speed, turning rates, and actuation effort is of interest for the next generation of underwater vehicle design. Integration of biological functional simplicity, robustness, and superior performance enables robotic vehicles to successfully complete difficult and dynamic operational goals. Gelatinous animals known as Cnidarians employ a wide variety of propulsive methods, ranging from the simple but efficient propulsion of large jellyfish to the rapid and highly maneuverable multi-jet propulsion of colonial animals known as siphonophores. This dissertation studies how these two extremes of underwater soft body propulsion are able to achieve simple yet effective control and locomotion, and thus inform the design of effective vehicle propulsion control and actuation. Two large single bell jellyfish robots, Cyro 2 and Cyro 3, were designed and constructed to implement the simple body form and propulsive methods of large jellyfish to study the unique locomotive characteristics and fluid interactions that generate straight swimming and turning maneuvers. The other extreme of small soft-body colonies moving by multi-jet propulsion was subsequently investigated in-depth, starting with a characterization of the biological fluid jetting actions and gaits. The results of these performance capabilities were then applied to an experimental robotic model with bio-inspired construction and controls to verify an elegant but highly functional neurological control scheme and the kinematic capabilities from varying jetting gait patterns.