This paper presents a covariance analysis of the performance of a Doppler-aided low-accuracy coarsely aligned strapdown inertial navigation system (INS), whose fine alignment takes place automatically in flight. It is shown that the fine alignment in azimuth, which requires turns, consists of in-flight gyro calibration and inflight gyrocompassing. The spacing of the turns is investigated. The influence of several position fixes is examined, and it is shown that they can replace INS turns. It is also shown that the use of magnetic heading reference reduces system errors but is not necessary for the satisfactory performance of the augmented system. Two suboptimal Kalman filters are designed and evaluated. Their small performance degradation with respect to that exhibited by the optimal filter and their low sensitivity to parameter changes is demonstrated by true covariance simulation runs.