An autonomous underwater vehicle 1 comprises mass conveying means operative to move a mass 4 along the longitudinal axis of the vehicle to a particular region such that a turning moment is produced to alter the pitch of the vehicle. Advantageously the pitch of the vehicle can be altered to the extent that the principal longitudinal axis of the vehicle is altered from being in a substantially horizontal plane to being in a substantially vertical plane and vice versa. Buoyancy of the vehicle can be adjusted by means of a movable pod 13 and a water tank 5. An electric motor 8 powered by battery units 7, which may comprise part of the moveable mass 4, drives a propulsor 2.
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