Abstract: A new type of inertial navigation system combining customary platform type with strap-down one is put forward. In this system the azimuth rate platform without azimuth stabilized loop, coordinate-resolver and azimuth syn chronzer is adopted. The azimuth angles of platform and vehicle will be obtained by an integrator from azimuth rate signals measured by an azimuth gyroscope supported on a horizontal gimbal. This type of inertial navigation system is suitable for vehicles without large-pitching maneuver, such as transports, aerodynamic and ballistic missiles.Operational principles of the azimuth rate platform, mechanization equations, distinguishing features of initial alignment, and calibration and compensation for drifts of gyroscopes are discussed in this paper. Error propagation characteristics caused by various error sources for navigation positioning, velocity and attitude are simulated on a digital computer. Simplicity in platform structure, small volume and weight, high reliability, possibility of calibration and compensation for drifts of the azimuth gyroscope are the distinctive advantages of this inertial navigation system.Moreover, by using a specific optical system referring to given azimuth angles of land marks and geographical latitudes, it is possible to accomplish not only fast alignment, but also calibration and compensation of horizontal gyroscope.