One of the many successful uses of the laser is as a rotation sensor. In the past, the usual approach in the design of gyroscopes was to use a spinning mass mounted on stable element, so that the gyroscope was fixed in inertial space and through the use of gimbals, isolated from the vehicle motion. With the advent of the laser, a clever implementation made use of a relatively little known physical mechanism to allow the laser to sense rotation. The rotation sensing is possible in the frame of the laser, thus allowing the device to be measured directly to the vehicle, and avoiding the need for gimbals. In that the laser was configured with a closed contour for the cavity, it has been commonly described as a ring laser gyro, or sometimes simply as a RLG. The RLG was first operated in 1962 and the past years, it has been investigated by many university and industrial laboratories. It was put into large scale production in 1978 by Honeywell, as a strap down inertial reference unit for aircraft applications. It is now considered a mature technology and there have been many publications describing the various form of its implementation. There have been two works which describe the development of the RLG from a historic standpoint.