Mobile targets, such as road mobile and rail mobile missiles
Fixed moderately hard targets, such as missile silos
Distributed targets, such as airfields or naval bases
Hard targets, such as deeply buried command structures
Superhard targets, such as facilities located beneath mountains
Conventional weapons might be able to address some of the missions currently assigned to nuclear weapons, but not all of them. Some targets, like missile silos and command and control structures, are sufficiently hard that no conventional weapon will have the energy to defeat them. Other targets, such as airfields and naval bases, are sufficiently dispersed that a massive amount of conventional explosives would be required for their destruction. Even though conventional weapons could damage or destroy such targets, they could do so today only over an extended time frame and with the use of limited resources that may be required in other theaters of operation. Future conventional weapons designs may change this, but there are still limits on the amount of damage that can be caused with a given quantity of high explosive. For these and other reasons, nuclear weapons are expected to continue to play a role in strategic doctrine, independent of their role as a psychological deterrent to aggression.
The United States employs a counterforce strategy that targets military assets that could inflict damage to our national interests. We do not threaten cities or populations as in a countervalue policy, although there is an implicit threat of doing so that is a potent element of the deterrent calculus. American nuclear weapons systems are designed to hold specific classes of targets at risk, using the minimum explosive forces necessary to accomplish the mission. However, a sizable factor governing the explosive force required to defeat a target of given hardness is the precision with which weapons can be delivered. The evolution of accurate delivery systems could change engagement strategies for nuclear weapons, in some cases reducing the required yield or even eliminating the need for an explosion at all. Once again, the use of conventional weapons presumes a level of detailed information on the location and characteristics of the target that has so far eluded military planners. A reliance on precision conventional munitions for some strategic missions presumes a major investment in intelligence collection and analysis tools, including accurate means of assessing target damage following an attack. This is particularly important for strategic targets such as mobile missiles or weapons of mass destruction that could, if they survive, inflict significant damage.”