Abstract: A water craft or land vehicle is stabilized against rolling and pitching forces by a mass or masses rotating about a vertical axis. The mass or masses are distributed along the vertical axis so that the center of the overall mass lies on the roll and pitch axes so that resistance to roll and pitch is exerted without precession. The gyro is gimballed along two axes which coincide with the roll and pitch axes. A stop mechanism allows a free pitching and rolling through a small angle before gyro resistance is met. Hydrofoils may be extended and retracted under pitch and roll signals from the gyro for extra stability.