For Nike, three radars were used. The acquisition radar (such as the AN/GSS-1 Electronic Search Central with the AN/TPS-1D radar) searched for a target to be handed over to the Target Tracking Radar (TTR) for tracking. The Missile Tracking Radar (MTR) tracked the missile by way of a transponder, as the missile's radar signature alone was not sufficient. The MTR also commanded the missile by way of pulse-position modulation, the pulses were received, decoded and then amplified back for the MTR to track. Once the tracking radars were locked the system was able to work automatically following launch, barring any unexpected occurrences. The computer compared the two radars' directions, along with information on the speeds and distances, to calculate the intercept point and steer the missile. The entirety of this system was provided by the Bell System's electronics firm, Western Electric.