This undated file photo released from North Korea's official Korean Central News Agency (KCNA) on August 25, 2016 shows North Korean leader Kim Jong-Un (C) laughing as he inspects a test-fire of strategic submarine-launched ballistic missile at an undisclosed location. Image Credit: AFP

New York: North Korea’s fifth nuclear test is ominous not only because the country is slowly mastering atomic weaponry, but because it is making headway in developing missiles that could hurl nuclear warheads halfway around the globe, threatening Washington and New York City.

The reclusive, hostile nation has been rushing to perfect missiles that are small, fast, light and surprisingly advanced, according to analysts and military officials. This spring and summer, Pyongyang successfully tested some of these missiles, while earlier efforts had fizzled or failed.

“They’ve greatly increased the tempo of their testing — in a way, showing off their capabilities, showing us images of ground tests they could have kept hidden,” John Schilling, an aerospace engineer and expert on North Korea’s missile program, said in an interview on Friday. “This isn’t something that can be ignored anymore. It’s going to be a high priority for the next president.”

Military experts say that by 2020, Pyongyang will most likely have the skills to make a reliable intercontinental ballistic missile topped by a nuclear warhead. They also expect that by then North Korea may have accumulated enough nuclear material to build up to 100 warheads.

Siegfried S. Hecker, a Stanford professor who has traveled to North Korea and who formerly directed the Los Alamos weapons lab in New Mexico, the birthplace of the atomic bomb, said North Korea’s progress in missile and nuclear development signals that it has gone from seeing unconventional weapons as bargaining chips to “deciding they need a nuclear weapons fighting force.”

The Pentagon warned Congress in a report earlier this year that one of Pyongyang’s latest missiles, if perfected, “would be capable of reaching much of the continental United States.”

In congressional testimony, American officials have provided more details. Intelligence analysts, they say, now judge that North Korea can miniaturise a nuclear weapon, place it atop a missile and fire it at the United States — though the odds of a successful nuclear strike are seen as low.

Adm. Samuel J. Locklear III, head of the Pacific Command, last year summed up the deep concern. “All the indications are that we have to be prepared to defend the homeland,” he told the Senate Armed Services Committee.

North Korea’s own claims about its nuclear capacities are generally viewed with extreme skepticism. The state, led by an erratic, young leader, Kim Jong-un, is notorious for blustering propaganda, fake photos and outright lies.

So private analysts and United States intelligence officials have in recent years tracked the country’s progress by studying carefully vetted imagery from satellites, and from North Korea itself, of the growing number of missile firings and engine tests. The experts track how far and fast the missiles travel, and the color of their plumes. Recently, one set of plumes became much cleaner, indicating the successful use of advanced propellants, analysts reported.

North Korea is an impoverished nation whose sophisticated missile programme has been built with Cold War-era Russian technology as well as the expertise of Russian engineers who moved there in the early 1990s looking for lucrative work after the Soviet Union fell apart, rocket experts and intelligence analysts say.

The Soviet Union, if poor in consumer goods, inaugurated the space age in dazzling firsts. Eventually, the United States caught up and won the race, landing astronauts on the moon. As it turns out, Russia’s rocket engines were far more innovative than those the Americans used.

Jeffrey Lewis, a North Korea specialist at the Middlebury Institute for International Studies at Monterey, in California, recently noted the grim implications of a test-firing on land that featured the debut of a powerful new engine.

“That means that, rather than simply hitting the West Coast, an operational North Korean ICBM could probably reach targets throughout the United States, including Washington, D.C.,” he wrote in a blog.

Pyongyang obtained its first wave of Russian rocket technology in the 1980s, giving it an ability to make Scuds, short-range missiles with engines that burn kerosene and emit smoky exhaust. Soon, the collapse of the Soviet rocket industry brought North Korea a second wave of far more potent technology.

The collapse began late in the Cold War as arms agreements led to deep cuts in both Soviet and American nuclear forces. It accelerated when Russia was unable to create a private industry for putting commercial satellites into orbit. Soon, impoverished rocket designers were fleeing Russia.

In one incident in late 1992, officials at a Moscow airport blocked a group of nearly two dozen missile experts, along with their wives and children, from traveling to Pyongyang, the North Korean capital. “I have always believed that our work is the most important,” Yuri Bessarabov, one of the rocket scientists, told Moscow News. “But it has turned out that we are unnecessary.”

By the time the US President Barack Obama took office, in January 2009, Pyongyang had deployed hundreds of short- and medium-range missiles that used motors of Russian design, and had exported hundreds of the weapons armed with conventional warheads to countries including Egypt, Iran and Syria. Typically, the countries bought Scuds.

At this time, North Korea was also developing the new generation of missiles powered by a much more advanced engine. Western intelligence analysts were alarmed to discover that the new engine derived from the R-27, a compact missile made for Soviet submarines that had carried a nuclear warhead. Its creator was the Makeyev Design Bureau, an industrial complex in the Ural Mountains whose rogue experts had been detained at the Moscow airport.

The engine jacked up heat, thrust and range, outpacing the Scud motor. And its propellants were more energetic than the old kerosene fuels. They were hypergolic. That meant the ingredients, when mixed, ignited spontaneously in powerful blasts. They made the smoky kerosene look archaic.

The engine was being developed to power a new missile known as the Musudan, named after Pyongyang’s main launching site. The greater thrust of its single engine translated into greater range. Analysts warned that the missile’s warhead might fly for up to 2,400 miles — far enough to hit the American base at Guam but shy of the minimum intercontinental range of 3,400 miles.

At a military parade in late 2010, Pyongyang unveiled its R-27 spinoff, giving substance to years of American intelligence warnings. The Musudan turned out to be 5 feet wide and 40 feet long — remarkably small compared to North Korea’s large missiles, which military analysis saw as sitting ducks.

The smaller missiles displayed that day were transported on trucks and could be hauled on country roads through forested regions or kept in tunnels, making them easy to hide and, as a target, difficult to find and destroy.

Pyongyang also used the R-27 engine design as a building block to make compact missiles that could fire warheads between continents.

The KN-08 missile (Korea North military type 8) was powered by two of the advanced motors. Analysts said its range was intercontinental and might send a warhead plummeting down on the West Coast. The KN-14, a longer version of the KN-08, appeared able, in theory, to send one of Pyongyang’s nuclear warheads crashing down on Washington, D.C.

Today, the KN-08 and the KN-14 are widely seen as the most threatening missiles in North Korea’s developing arsenal, especially given the land test in April of the potent engine that apparently powers them.

Still, experts note that North Korea is years away from deploying a reliable long-range missile. For instance, it has yet to master the complex technology needed to protect a nuclear warhead from the searing heat generated as it plunges from outer space to a fiery re-entry.

Experts also do not see North Korea as being capable anytime soon of building a much more destructive hydrogen warhead, capable of destroying large cities.

Still, military officials worry about a day of reckoning.

“The intel community assesses North Korea’s ability to successfully shoot an ICBM with a nuclear weapon and reach the homeland as low,” William E. Gortney, commander of North American Aerospace Defence Command, told a subcommittee of the Senate Armed Services Committee in April.

Eventually, he added, “we assess that this low probability will increase,” and the United States will need to invest in better defenses.

Making sure Pyongyang has serious doubts about whether a nuclear strike would ever succeed, Commander Gortney added, “is absolutely critical.