In January, the New York Times reported: As North Korea dug tunnels at its nuclear test site last fall, watched by American spy satellites, the Obama administration was preparing a test of its own in the Nevada desert.

A fighter jet took off with a mock version of the nation’s first precision-guided atom bomb. Adapted from an older weapon, it was designed with problems like North Korea in mind: Its computer brain and four maneuverable fins let it zero in on deeply buried targets like testing tunnels and weapon sites. And its yield, the bomb’s explosive force, can be dialed up or down depending on the target, to minimize collateral damage.

In short, while the North Koreans have been thinking big — claiming to have built a hydrogen bomb, a boast that experts dismiss as wildly exaggerated — the Energy Department and the Pentagon have been readying a line of weapons that head in the opposite direction.

The build-it-smaller approach has set off a philosophical clash among those in Washington who think about the unthinkable.

Mr. Obama has long advocated a “nuclear-free world.” His lieutenants argue that modernizing existing weapons can produce a smaller and more reliable arsenal while making their use less likely because of the threat they can pose. The changes, they say, are improvements rather than wholesale redesigns, fulfilling the president’s pledge to make no new nuclear arms.

But critics, including a number of former Obama administration officials, look at the same set of facts and see a very different future. The explosive innards of the revitalized weapons may not be entirely new, they argue, but the smaller yields and better targeting can make the arms more tempting to use — even to use first, rather than in retaliation. [Continue reading…]