Complex sentence: The earliest laser guidance seekers measured the reflected laser light at four corners of the seeker window, with the seeker actuating the control fins to steer the weapon in the direction of the strongest signal return, thereby keeping the weapon centered on the laser sparkle.
Split into simpler sentences: The earliest laser guidance seekers measured the reflected laser light at four corners of the seeker window. The seeker actuated the control fins to steer the weapon in the direction of the strongest signal return, thereby keeping the weapon centered on the laser sparkle.