decapitation strike or a countervalue strike, a counterforce strike might result in a potentially more constrained retaliation. Though the Minuteman III of the mid-1960s was MIRVed with three warheads, heavily MIRVed vehicles threatened to upset the balance; these included the SS-18 Satan which was deployed in 1976, and was considered to threaten Minuteman III silos, which led some neoconservatives to conclude a Soviet first strike was being prepared for. This led to the development of the aforementioned Pershing II, the Trident I and Trident II, as well as the MX missile, and the B-1 Lancer. MIRVed land-based ICBMs are considered destabilizing because they tend to put a premium on striking first. When a missile is MIRVed, it is able to carry many warheads (up to eight in existing US missiles, limited by New START, though Trident II is capable of carrying up to 12) and deliver them to separate targets. If it is assumed that each side has 100 missiles, with five warheads each, and further that each side has a 95 percent chance of neutralizing the opponent's missiles in their silos by firing two warheads at each silo, then the attacking side can reduce the enemy ICBM force from 100 missiles to about five by firing 40 missiles with 200 warheads, and keeping the rest of 60 missiles in reserve. As such, this type of weapon was intended to be banned under the START II agreement; however, the START II agreement was never brought into force, and neither Russia nor the United States ratified the agreement. Late Cold War The original US MAD doctrine was modified on July 25, 1980, with US President Jimmy Carter's adoption of countervailing strategy with Presidential Directive 59. According to its architect, Secretary of Defense Harold Brown, "countervailing strategy" stressed that the planned response to a Soviet attack was no longer to bomb Soviet population centers and cities primarily, but first to kill the Soviet leadership, then attack military targets, in the hope of a Soviet surrender before total destruction of the Soviet Union (and the United States). This modified version of MAD was seen as a winnable nuclear war, while still maintaining the possibility of assured destruction for at least one party. This policy was further developed by the Reagan administration with the announcement of the Strategic Defense Initiative (SDI, nicknamed "Star Wars"), the goal of which was to develop space-based technology to