SEOUL — Pride and jealousy have driven North and South Korea to engage in propaganda shouting matches and compete over who could build a taller flagpole on their border. Now that one-upmanship is intensifying a much more dangerous side of their rivalry: the arms race.
Earlier this month, South Korea’s dream of building its own supersonic fighter jet was realized when it unveiled the KF-21, developed at a cost of $7.8 billion. The country also recently revealed plans to acquire dozens of new American combat helicopters. When President Moon Jae-in visited the Defense Ministry’s Agency for Defense Development last year, he said South Korea had “developed a short-range ballistic missile with one of the largest warheads in the world.”
Unlike North Korea, the South lacks nuclear weapons. But in recent years the country has revved up its military spending, procuring American stealth jets and building increasingly powerful conventional missiles capable of targeting North Korean missile facilities and war bunkers.
The impoverished North has used those moves to justify expanding its own arsenal, and has threatened to tip its short-range missiles with nuclear warheads and make them harder to intercept. Experts warn that the ensuing arms race between the two countries is jeopardizing the delicate balance of peace on the Korean Peninsula.
“As both sides act and react through arms buildups in the name of national defense, it will create a vicious cycle that will eventually undermine their defense and deepen their security dilemma,” said Jang Cheol-wun, an analyst at the Korea Institute for National Unification, a government-funded research group.
The two Koreas have long been locked in a perpetual arms race. But Pyongyang’s growing nuclear capabilities, coupled with the fear of a withdrawal of American troops from South Korea under President Donald J. Trump, added to those tensions.
While in office, Mr. Moon has increased South Korea’s annual military spending by an average of 7 percent, compared with the 4.1 percent average of his predecessor. After diplomacy failed to eliminate the North’s nuclear arsenal, Mr. Moon had to reassure South Koreans that their country was not a “sitting duck,” said Yoon Suk-joon, a researcher at the Korea Institute for Military Affairs.
Soon after Mr. Moon’s visit to the Agency for Defense Development, South Korean media reported that the weapon he referred to was the Hyunmoo-4, a missile tested last year. According to missile experts, the Hyunmoo-4 can fly 497 miles, enough to target all of North Korea. Its two-ton payload — unusually large for a short-range missile — could destroy the North’s underground missile bases.
Whether it could destroy the deep bunkers into which Kim Jong-un, the North’s leader, would retreat in wartime depends on how deeply they are buried. According to missile experts, though, South Korea would likely need earth-penetrating nuclear weapons from the United States to destroy such prized targets.
Not to be outdone, on March 25 North Korea launched a new ballistic missile of its own and said the weapon flew 372 miles with a 2.5-ton warhead. The test prompted Mr. Moon to claim the following day that South Korea had “world-class missile capabilities, enough to defend ourselves while abiding by our commitment to make the Korean Peninsula free of nuclear weapons.”
Washington has tried to prevent missile proliferation on the Korean Peninsula for decades. Under guidelines first adopted between Washington and Seoul in 1979, South Korea was barred from developing ballistic missiles with a range of more than 187 miles and a payload of more than 1,100 pounds. After North Korea attacked a South Korean island with a rocket barrage in 2010, South Korea demanded that Washington ease the restrictions so it could build more powerful missiles.
“We hinted that we might scrap the missile guidelines unilaterally,” said Chun Yung-woo, the national security adviser at the time. “We told the Americans that if we didn’t address concern over the North’s growing nuclear and missile threat, more and more South Koreans would call for building nuclear bombs for ourselves.”
In 2012, Washington agreed to let South Korea deploy ballistic missiles with a range of up to 497 miles as long as it abided by the 1,100-pound warhead limit. It also said South Korea could exceed the payload limit by several times on missiles with shorter ranges.
South Korea has since tested missiles with growing ranges and bigger warheads, including the Hyunmoo-2A, Hyunmoo-2B and Hyunmoo-2C. Once North Korea launched its first intercontinental ballistic missile in 2017, Mr. Trump lifted the payload limit entirely, making way for the Hyunmoo-4.
Ever since taking power a decade ago, Mr. Kim has tried to build ICBMs capable of reaching the United States. But he has also threatened to tip the missile balance against South Korea.
In January, he indicated that his country had already built short-range nuclear missiles aimed at South Korea and vowed to improve them by making the warheads “smaller, lighter and tactical.” South Korea’s strategy of deterrence has been based on the belief that the best chance it has against the North without nuclear weapons of its own is to build up a conventional missile defense and deploy ever more powerful “bunker busters” to make Mr. Kim fear for his life.
When North Korea tested its intercontinental ballistic missile in 2017, the United States and South Korea responded by launching their own ballistic missiles to demonstrate their “deep-strike precision” capabilities. In his book “Rage,” the journalist Bob Woodward wrote that the American missile traveled the exact distance between its launching point and the location from which Mr. Kim watched his I.C.B.M. launch.
Mr. Kim halted all missile tests in 2018, the year of the first of his two summit meetings with Mr. Trump. After their talks collapsed, North Korea resumed tests in 2019, rolling out three short-range ballistic missiles that were designed to counter the allies’ antimissile capabilities.
North Korea’s old fleet of Scud and Rodong missiles used liquid fuel and lacked precision. The country’s new generation of missiles uses solid propellants, making them quicker to launch, easier to transport and more difficult to target. They also have greater accuracy and evasive maneuvering power that could confound the South’s missile defense systems.
The new solid-fuel ballistic missile North Korea tested in March likely evaded the allies’ radar during its low-altitude maneuvering, leading the South Korean military to estimate its range at 280 miles, not the 372 miles the North claimed, said Chang Young-keun, a missile expert at Korea Aerospace University. Mr. Chang said the missile could also likely increase range and warhead weight because it was powered by “the largest solid-fuel rocket motor developed and tested in North Korea so far.”
The North’s ICBMs still use liquid fuel, which takes hours to load before launching, making them vulnerable to American pre-emptive strikes. But in his January speech, Mr. Kim vowed to build solid-fuel ICBMs, presenting an even bigger challenge for American missile defenses. Such prospects deepen the fear among some South Koreans that Washington would be less likely to intervene if it, too, faced a possible North Korean nuclear attack.