Washington: Concerned that the missile defence system designed to protect US cities is insufficient by itself to deter a North Korean attack, the Trump administration is expanding its strategy to also try to stop Pyongyang’s missiles before they get far from Korean airspace.

The new approach, hinted at in an emergency request to Congress last week for $4 billion (Dh14.69 billion) to deal with North Korea, envisions the stepped-up use of cyberweapons to interfere with the North’s control systems before missiles are launched, as well as drones and fighter jets to shoot them down moments after lift-off.

The missile defence network on the West Coast would be expanded for use if everything else fails.

In interviews, defence officials, along with top scientists and senior members of Congress, described the accelerated effort as a response to the unexpected progress that North Korea has made in developing intercontinental ballistic missiles capable of delivering a nuclear weapon to the continental United States.

“It is an all-out effort,” said Sen. Jack Reed of Rhode Island, the top Democrat on the Senate Armed Services Committee, who returned from a lengthy visit to South Korea last month convinced that the United States needed to do far more to counter North Korea. “There is a fast-emerging threat, a diminishing window, and a recognition that we can’t be reliant on one solution.”

For years, that single solution has been the missile batteries in Alaska and California that would target any long-range warheads fired toward the US mainland, trying to shoot them down as they re-enter the atmosphere. Such an approach, known as “hitting a bullet with a bullet,” remains of dubious effectiveness, even after more than $100 billion has been spent on the effort. Anti-missile batteries on ships off the Korean coast and in South Korea protect against medium-range missiles but not those aimed at US cities.

So the administration plans to pour hundreds of millions of dollars into the two other approaches, both of which are still in the experimental stage. The first involves stepped-up cyberattacks and other sabotage that would interfere with missile launches before they occur — what the Pentagon calls “left of launch.” The second is a new approach to blowing up the missiles in the “boost phase,” when they are slow-moving, highly visible targets.

The $4 billion emergency budget sought by the White House is on top of the $8 billion that the Missile Defence Agency has already been granted for this fiscal year, as well as what other military services and agencies are putting into missile defence. Another $440 million was moved from existing programs to anti-missile work two months ago, as the North Korea threat became more serious.

In the emergency request to Congress, and in documents made public by its committees, the precise use of the funds is cloaked in deliberately vague language.

Hundreds of millions of dollars, for example, are allotted for what the documents called “disruption/defeat” efforts. Several officials confirmed that the “disruption” efforts include another, more sophisticated attempt at the kind of cyber and electronic strikes that President Barack Obama ordered in 2014 when he intensified his efforts to cripple North Korea’s missile testing.

Using cyberweapons to disrupt launches is a radical innovation in missile defence in the past three decades. But in the case of North Korea, it is also the most difficult. It requires getting into the missile manufacturing, launch control and guidance systems of a country that makes very limited use of the internet and has few connections to the outside world — most of them through China and, to a lesser degree, Russia.

In the operation that began in 2014, a range of cyber and electronic-interference operations were used against the North’s Musudan intermediate-range missiles, in an effort to slow its testing. But that secret effort had mixed results.

Congressional documents also talk of making “additional investments” in “boost-phase missile defence.”

The goal of that approach is to hit long-range missiles at their point of greatest vulnerability — while their engines are firing and the vehicles are stressed to the breaking point, and before their warheads are deployed.

Defence Secretary Jim Mattis is also weighing, among other boost-phase plans, formulas that draw on existing technologies and could be deployed quickly.

One idea is having stealth fighters such as the F-22 or the F-35 scramble from nearby bases in South Korea and Japan at the first sign of North Korean launch preparations. The jets would carry conventional air-to-air missiles, which are 12 feet long, and fire them at the North Korean long-range missiles after they are launched. But they would have to fly relatively close to North Korea to do that, increasing the chances of being shot down.

A drawback of boost-phase defence is the short window to use it. Long-range missiles fire their engines for just five minutes or so, in contrast to warheads that zip through space for about 20 minutes before plunging back to Earth. And there is the risk of inviting retaliation from North Korea.

“You have to make a decision to fire a weapon into somebody’s territory,” Gen. John E. Hyten of the Air Force, commander of the US Strategic Command, which controls the US nuclear missile fleet, recently told a Washington group. “And if you’re wrong, or if you miss?”

A boost-phase idea getting much notice would be to have drones patrol high over the Sea of Japan, awaiting a North Korean launch. Remote operators would fire heat-sensing rockets that lock onto the rising missiles.

“It’s a huge advance,” Gerold Yonas, chief scientist for President Ronald Reagan’s Star Wars programme, said of the drone plan. “It’s one of those things where you hit yourself on the forehead and say, ‘Why didn’t I think of that?’”