Abstract: A four-axis gyro stabilized inertial reference system. The system comprises a nested gimbal configuration, which includes a platform and three successively larger and concentrically disposed inner, middle and outer gimbals and an outer casing. The platform and inner, middle and outer gimbals are each configured to permit rotation about an associated axis with that axis being perpendicular to the corresponding axis of the neighboring gimbal or platform. The system further includes a platform stabilizing means for maintaining the platform in a substantially fixed spatial orientation, independent of the spatial orientation of the outer casing and over a predetermined range of angular rates.