Autonomous Underwater Vehicles (AUVs) are a developing technology with multiple applications including oceanographic research, military missions and commercial activities such as oil and gas field exploration. The reported research covers two main areas, namely, the assessment of the survey performance of AUVs and the development of the next generation of multi-purpose AUVs. The performance characteristics of long range survey-style AUVs are examined and improvements in performance are sought through the use of hybrid devices. Hybrid devices are defined as those that provide both propulsion and manoeuvring forces. Two devices were chosen for detailed investigation; a vectored thruster and a collective and cyclic pitch propeller. The manoeuvring performance of both devices was found to be insufficient to justify the additional engineering complexity associated with them. The aim of the next generation of AUVs is to be able to combine long range survey capabilities with low speed investigation of the environment encountered. An assessment of a likely mission profile and a review of the available design options demonstrate that maintaining the survey efficiency of the AUV is of principal importance. Therefore the investigation focuses on approaches to the addition of low speed control to an existing survey-style AUV design using propeller based thrusters. Externally mounted thrusters and through-body tunnel thrusters are reviewed and new experimental investigations are reported to provide insight into the performance characteristics on a survey-style AUV hull form. The main body of the experimental programme characterises forward and aft mounted tunnel thruster performance over a range of forward speeds and small yaw angles. The results are used to develop a new, simple modelling procedure representing the performance of tunnel thrusters on an AUV which facilitates the incorporation of the characteristics of tunnel thrusters into numerical simulations of AUV performance. Such a simulation is used to examine approaches to undertaking the transition phase between high speed survey and low speed manoeuvring operation. The results demonstrate the advantageous nature of undertaking a smooth interchange between control approaches considering both the vehicle performance and the energy demands.