An electric motor for powering a submersible vehicle under water is disclosed. The motor has a housing with resilient seals for resisting the passage into the housing and motor of surrounding seawater. A liquid substantially fills all voids in the motor and housing, so that even under substantial external pressure at substantial depths under surrounding water the liquid within the motor and motor housing voids will support the seals against failure and prevent the surrounding water from leaking into the motor and motor housing. The vehicle has a housing within which there is a void which is substantially filled with a liquid There is an opening in the housing wall and a resilient member such as a flexible, resilient tube or diaphragm is disposed within the opening and is in fluid communication with both the interior and exterior of said housing, so that the pressure on the interior and exterior of said housing will be equalized.