Artificial neural networks offer an alternative strategy for the nonlinear control of unmanned underwater vehicles (uuvs). This paper investigates the use of a multi-layered perceptron (MLP) network in controlling an uuv over a sea-bed profile and compares the use of applying chemotaxis learning to that of the more commonly employed back propagation algorithm. The results show that, for differing sized MLPS, the chemotaxis algorithm produces a successful controller over the sea-bed profile in an improved training time. Also it will be shown that, in the presence of noise and change in vehicle mass, the neural controller out-performed a classical proportional-integral-derivative controller.i. I N T R O D U C T I O N . The control of uuvs has always offered a challenge to the control engineer due to the combined nonlinear nature of both the vehicle itself and the environment in which it operates. Whilst the traditional tethered remotely operated vehicle (ROV) frequently employs a human pilot in the loop, there has been a drive towards giving the vehicle some form of autonomy to remove the responsibility for die dynamic control from the operator and providing the ROV with a limited autonomous capability via an autopilot.uuvs are currently at the centre of considerable research interest in both the commercial and military sectors. They offer advantages over ROVS in terms of flexibility of use (range and depth) and can replace vulnerable human divers or expensive manned submersibles. Techniques including gain-scheduling, sliding mode and fuzzy logic have all been considered for use in uuv control and these are reviewed in Farbrother and Stacy. 1 The applications of neural networks to the dynamic control of uuvs has received a certain amount of attention. 2 ' 3 Generally these have considered midwater control for heading and depth-keeping, however, one further important area which has drawn minimal consideration is that of bottom profiling. For tasks such as pipe inspection, oceanographic surveying and mine deployment, some form of sea-bed profiling is required and, in such cases, the uuv has to maintain a safe height above the bottom. Thus, herein, are reported the results of a study into the application of neural networks to control an uuv in the sea-bed profiling mode. Also results are presented to show the capability of the neural controller to cope with noisy sensor signals and a change in vehicle mass during a simulated mission.A particular feature of the work herein is the employment of the chemotaxis 292