HOUSE OVERSIGHT 028669 invasion by striking targets in the Soviet Union and Eastern Europe, North Korea presumably plans to defend itself, should war erupt on the peninsula, by threatening U.S. regional allies and targets in the United States. North Korea's mission requires small, lightweight warheads, and missiles that work -- and the only way to know that they work is to test them. So far, the weapons have proved unspectacular. The country's first nuclear test, conducted in 2006, was an embarrassment. Pyongyang had told the Chinese that the device would generate four kilotons of explosive power, but it ended up producing less than one. The second test in 2009 fared slightly better, producing between one and eight kilotons, although it is not known what size of a blast the North Koreans had sought. Moreover, Pyongyang has much more work to do before it can boast weapons that will actually fit on its missiles (which have been, themselves, a series of humiliating failures). Observers in the West who presume that North Korea's behavior must be about signaling should remember NATO and the United States' own experience during the Cold War. The United States understood then that the ability to conduct nuclear operations was the very foundation of a credible deterrence strategy. Today, a sound strategy for dealing with North Korea should not ascribe ulterior motives to acts that the United States once considered rational and routine. The view that nuclear weapons are merely political instruments -- suitable for sending signals, but not waging wars -- is now so common in Washington, London, and Berlin that it is hard to find anyone who disagrees. Yet those comforting assumptions are not shared by leaders everywhere. Beyond North Korea, Russia is cutting down its arsenal, modernizing the nuclear forces it plans to keep, and increasing its reliance on nuclear weapons in national defense strategy. China is slowly expanding its own arsenal, while