An approach is proposed for substantiation of the requirements for the use of the means of control of a technical state and diagnostics of failures of the electro-pneumatic steering gear with a hydraulic brake for the autonomous underwater vehicles. The extreme requirements are based on the use and means of control of a technical state and diagnostics of failures of the electro-pneumatic steering gear with a hydraulic brake for the autonomous underwater vehicles. Using the methods of the system analysis, a decomposition of the extreme requirements up to the level of the control functions and diagnostics of the steering gear was carried out. The methods and algorithms for control and diagnostics of the steering gear, a set of technological control and test equipment were developed. The novelty of the developed methods and algorithms for the control and diagnostics of the steering gear of the autonomous underwater vehicles is related to the formalization of the process of justification of the requirements to the use of the autonomous underwater vehicles, with transition from the requirements to the functions of the devices and, further, to the methods and algorithms of control and diagnostics of the steering gear. This allows us to reduce the probability of making wrong decisions at the stage of development of the equipment, which are the most frequent and lead to a significant increase of the cost and time of the research and development, and also create the technological equipment, methods and algorithms for control of the technical state and diagnostics of failures of a new type of the hybrid actuators - the elec-tropneumatic steering gear with a hydraulic brake. For testing of the proposed approach an autonomous unmanned underwater vehicle, which moves in water at a depth up to 30 m with velocities over 100 km per hour, was considered. The control of the autonomous underwater vehicle is performed by two pairs of rudders, which, depending on the driving mode of the device, take position from 0 to 90 degrees relative to the vehicle hull.