of the Cold War, including some in the USSR's own leadership. Other evidence of this comes from the Soviet minister of defense, Dmitriy Ustinov, who wrote that "A clear appreciation by the Soviet leadership of what a war under contemporary conditions would mean for mankind determines the active position of the USSR." The Soviet doctrine, although being seen as primarily offensive by Western analysts, fully rejected the possibility of a "limited" nuclear war by 1975. Criticism Deterrence theory has been criticized by numerous scholars for various reasons. A prominent strain of criticism argues that rational deterrence theory is contradicted by frequent deterrence failures, which may be attributed to misperceptions. Scholars have also argued that leaders do not behave in ways that are consistent with the predictions of nuclear deterrence theory. For example, scholars have argued that it is inconsistent with the logics of rational deterrence theory why states that have achieved second-strike capabilities continue to build nuclear arsenals once they have reached the second-strike threshold. Challengeable assumptions Second-strike capability A first strike must not be capable of preventing a retaliatory second strike or else mutual destruction is not assured. In this case, a state would have nothing to lose with a first strike, or might try to preempt the development of an opponent's second-strike capability with a first strike. To avoid this, countries may design their nuclear forces to make decapitation strike almost impossible, by dispersing launchers over wide areas and using a combination of sea-based, air-based, underground, and mobile land-based launchers. Another method of ensuring second strike capability is through the use of dead man's switch or "fail-deadly:" in the absence of ongoing action from a functional command structure—such as would occur after suffering a successful decapitation strike—an automatic system defaults to launching a nuclear strike upon some target. A particular example is the Soviet (now Russian) Dead Hand system, which is a semi-automatic "version of Dr. Strangelove's Doomsday Machine" which, once activated, can launch a second strike without human intervention. The purpose of the Dead Hand system is to ensure a second strike even if Russia were to suffer a decapitation attack, thus maintaining MAD. Perfect detection No false positives (errors) in the equipment and/or procedures that must identify a launch by the other side. The implication of this is that an accident could lead to a full nuclear exchange. During the Cold War there were several instances