A method is provided for guiding a mortar projectile fired longitudinally from a launcher along a ballistic trajectory. The method includes providing a first inertial navigation system (INS), a laser emitter and optical sensor on the launcher, providing a second INS and a laser reflector on the projectile, and presetting the second INS to an initial reference position prior to firing the projectile. Subsequent to launch, the method further includes emitting a longitudinally directed laser beam from the emitter to the reflector; receiving the reflected signal to the optical sensor; establishing a position and velocity of the projectile based on the reflected signal; transmitting a correction signal to the projectile from the launcher; resetting the second INS at a position prior to reaching maximum altitude; and guiding the projectile along the trajectory by adjusting control fin orientation.