But other experts have grown increasingly skeptical of the new approach, arguing that manufacturing errors, disgruntled insiders, and sheer incompetence can also send missiles awry. In the past eight months, they note, the North has managed to successfully launch three medium-range rockets. And Kim Jong Un, the North Korean leader, now claims his country is in “the final stage in preparations” for the inaugural test of intercontinental missiles — perhaps a bluff, perhaps not.

Soon, a large number of the North’s military rockets began to explode, veer off course, disintegrate in midair, and plunge into the sea. Advocates of such efforts say they believe that targeted attacks gave US antimissile defenses a new edge and delayed by several years the day when North Korea will be able to threaten US cities with nuclear weapons launched on intercontinental ballistic missiles.

WASHINGTON — Three years ago, President Obama ordered Pentagon officials to step up their cyber and electronic strikes against North Korea’s missile program in hopes of sabotaging test launches in their opening seconds.

An examination of the Pentagon’s disruption effort, based on interviews with Obama and Trump administration officials as well as a review of extensive but obscure public records, found the United States still doesn’t have the ability to effectively counter North Korean nuclear and missile programs. Those threats are far more resilient than many experts thought and pose such a danger that Obama, as he left office, warned President Trump they were likely to be the most urgent problem he would confront.


Trump has signaled his preference to respond aggressively to the North Korean threat. In a Twitter post after Kim first issued his warning on New Year’s Day, the president wrote, “It won’t happen!” Yet like Obama before him, Trump is quickly discovering he must choose from highly imperfect options.


He could order the escalation of the Pentagon’s cyber and electronic warfare effort, but that carries no guarantees. He could open negotiations with the North to freeze its nuclear and missile programs, but that would leave a looming threat in place. He could prepare for direct missile strikes on the launch sites, which Obama also considered, but there is little chance of hitting every target. He could press the Chinese to cut off trade and support, but Beijing has always stopped short of steps that could lead to the regime’s collapse.

The decision to intensify the cyber and electronic strikes, in early 2014, came after Obama concluded that the $300 billion spent since the Eisenhower era on antimissile systems, often compared to hitting “a bullet with a bullet,” had failed the core purpose of protecting the United States. Flight tests of interceptors had a failure rate of 56 percent, under near-perfect conditions. Privately, experts warned the system would fare worse in real combat.

So the Obama administration searched for a better way to destroy missiles. It reached for techniques the Pentagon had long been experimenting with under the rubric of “left of launch” because the attacks begin before the missiles ever reach the launchpad. For years, the Pentagon’s most senior officers and officials have publicly advocated these kinds of sophisticated attacks in little-noticed testimony to Congress and at defense conferences.

The approach taken in targeting the North Korean missiles has distinct echoes of the US- and Israeli-led sabotage of Iran’s nuclear program, the most sophisticated known use of a cyberweapon to attack a nuclear threat. It was effective for several years, until the Iranians figured it out and recovered. And Iran posed a relatively easy target: an underground nuclear enrichment plant that could be attacked repeatedly.


In North Korea, the target is much more challenging. Missiles are fired from multiple launch sites around the country and moved on mobile launchers in an elaborate shell game.

Advocates of the sophisticated effort to remotely manipulate data inside North Korea’s missile systems argue the United States has no real alternative because the effort to stop the North from learning the secrets of making nuclear weapons has already failed.

In February 2013, the North set off a nuclear test that yielded an explosion roughly the size of the bomb that leveled Hiroshima. Days afterward, the Pentagon announced an expansion of its force of antimissile interceptors in California and Alaska. It also began to unveil its “left of launch” program to disable missiles before liftoff.

General Martin E. Dempsey, the chairman of the Joint Chiefs of Staff, announced the program, saying that “cyberwarfare, directed energy and electronic attack,” a reference to such things as malware, lasers and signal jamming, were all becoming important new adjuncts to the traditional ways of deflecting enemy strikes.

Nonetheless, Kim has pressed ahead. Last April, North Korean engineers successfully fired off a matched pair of potent engines that could ultimately hurl warheads at the United States. In September, North Korea successfully tested a nuclear weapon with more than twice the destructive force of the Hiroshima bomb.


But a decision to go after an adversary’s launch ability can have unintended consequences, experts warn. Once the United States uses cyberweapons against nuclear launch systems — even in a threatening state like North Korea — Russia and China may feel free to do the same, targeting US missiles.

Some strategists say all nuclear systems should be off-limits for cyberattack. “I understand the urgent threat,” said Amy Zegart, a Stanford University intelligence and cybersecurity expert. “But 30 years from now, we may decide it was a very, very dangerous thing to do.”