 In December 1979 the higher-yield W78 warhead (335–350 kilotons) began replacing a number of the W62s deployed on the Minuteman-IIIs.These were delivered in the Mark 12A reentry vehicle.A small, unknown number of the previous Mark 12 RVs were retained operationally, however, to maintain a capability to attack more-distant targets in the south-central Asian republics of the USSR (the Mark 12 RV weighed slightly less than the Mark 12A).