A method for attitude alignment of a slave inertial measurement system connected to a rotationally mobile platform supported by a vehicle that is stationary relative to a reference navigation frame comprises the steps of mounting a master reference inertial measurement system on the rotationally mobile platform and determining a master reference system attitude using measurements of acceleration and angular rates of the master reference inertial measurement system relative to the reference navigation frame. A slave system attitude is determined using measurements of acceleration and angular rates of the slave inertial measurement system relative to a slave system navigation reference frame and comparing the slave system attitude to the master reference system attitude to determine an attitude difference. The attitude difference is processed to obtain a correction to the slave system attitude.