Most AUVs and Remotely Operated Vehicles (ROVs) use propellers to provide thrust, despite the manoeuvring difficulties this causes. Biologically inspired designs provide an alternative solution, and are growing in popularity due to the increased efficiency and manoeuvrability. A biologically inspired flapping foil propulsion system was designed, using LilyPad Computational Fluid Dynamics (CFD) Solver, to simulate the wake of a pair of interacting foils. Compared to a single foil, interacting foils provide increased thrust, and hence efficiency gains. The foil design was completed in tandem with the concept design of an AUV, rated to 100 m depth. A turtle inspired design allowed space to contain a payload which could document the ocean floor. A drop weight system was developed to allow the AUV to dive and resurface. The AUV was controlled with odometry, using an Arduino as the communication interface. Material testing was completed on a range of composite sandwich structures and cores, to determine a hull material which could be rated to 100m. Finite Element Analysis testing of the hull, foils and mechanism was also completed. A demonstrator was built to be tested up to a depth of 3.5 m in Towing Tanks at the University of Southampton. Experiments, including flapping frequency, straight line speed, turning circle, dive and resurface tests, and self-righting tests were performed. These validated the work completed during the simulations, and proved the concept of flapping foils as a propulsion mechanism with high manoeuvrability.