to political intentions from counterforce to countervalue, or any mix/withhold strategy to control escalation. Schlesinger described the doctrine as having three main aspects: The National Command Authority or its successors should have many choices about the use of weapons, always having an option to escalate. Targeting should make it very explicit that the first requisite is selective retaliation against the enemy's military (i.e., tailored counterforce). Some targets and target classes should not be struck, at least at first, to give the opponent a rational reason to terminate the conflict. Reduced collateral damage was another benefit of this "withhold" method. The SIOP policy was further modified during the Carter presidency under Presidential Directive 59, a key section of which stated The employment of nuclear forces must be effectively related to operations of our general purpose forces. Our doctrines for the use of forces in nuclear conflict must insure that we can pursue specific policy objectives selected by the National Command Authorities at that time, from general guidelines established in advance. (S) PD59 explored a "warfighting" doctrine that suggested that nuclear plans might change during a war, and that nuclear weapons were to be used in combination with conventional weapons. Carter's Secretary of Defense, Harold Brown, emphasized selective counterforce, but also explicitly threatened the Soviet leadership themselves. Major improvements in U.S. command, control, communications and intelligence (C3I), including making elements survivable during a nuclear war, were instituted to make the PD-59 doctrine feasible. Although secret NATO guidelines reportedly limited the size of nuclear weapons that the alliance could use on its territory to 10 kilotons, and prohibited their use in urban NATO areas, by 1982 SIOP-5 contained more than 40,000 possible targets in four categories: Soviet nuclear forces. Examples: ICBM launch centers and control facilities, bomber airfields, ballistic-missile submarine bases. Conventional forces. Examples: Supply depots, conventional airfields, ammunition storage, tank storage yards. Military and political centers. Examples: Command posts, communications facilities. Economic and industrial centers. Examples: Factories for ammunition and tanks, refineries, steel and aluminum plants, power plants. Whether Soviet military doctrine recognized the difference between counterforce and a general attack was unknown. A 1982 analysis stated, however, that the technically inferior Soviet attack-assessment system would likely have difficulty in differentiating between such attacks. In any case, given that the majority of Soviet nuclear airfields and missile sites were located west of the Ural mountains, many in major population centers, the analysis