The North Koreans are making a show of backing up their threats to counter what they call “the war provocations of the U.S. and South Korea.” 

On the first full day of the largest joint American-South Korean war games in five years, the North test-fired two submarine-launched ballistic missiles that flew 930 miles before landing in waters between North Korea and Japan, Pyongyang’s Korean Central News Agency reported. KCNA said the missiles reached their targets after doing figure-eights for two hours. 

The nature of the flights indicated the missiles were carefully controlled from the moment they were fired from a submarine — perfect, if done correctly, for zeroing in on relatively small targets. 

The testing of the two SLBMs, confirmed by American and South Korean forces, was in keeping with the vow of the North’s Workers Party to take “important practical steps for making more effective, powerful and offensive use of the war deterrent.” 

The statement, carried in English by KCNA, did not specify the nature of the deterrent, but it’s obvious the reference was to the North’s nuclear weapons, probably tactical nukes for specific targets. A submarine, capable of carrying a nuclear-tipped SLBM, could maneuver close to the target without being seen. 

The KCNA report reflected the pride of the North Korean leader, Kim Jong-un, who rules as general secretary of the party, in perfecting the SLBM, which the North last tested in October. 

“The drill confirmed the reliability of the weapon system and examined the underwater-to-surface offensive operations,” KCNA said. Submarines “constitute ones of other major forces of the DPRK nuclear deterrent,” it said, using DPRK for the North’s formal name, Democratic People’s Republic of Korea. 

That KCNA reported on the SLBM in English made clear the test was timed for intimidation during American and Korean exercises that show the tightness of their alliance since the election of the conservative Yoon Sul-yeol as president a year ago. Mr. Yoon’s interest in joint war games contrasts with the search by his liberal predecessor, Moon Jae-in, for accommodation with the North.

KCNA said America and South Korea were “reaching the red line” — an American term for the line beyond which the enemy should not go without risking warfare. Aside from missile tests and rhetoric, however, there were no signs the North was gearing for war. 

Mr. Kim has been itching to counter the American and South Korean exercises for the past week. Several days ago, accompanied by his young daughter Ju-ae, he offered what was called “field guidance” at a drill of artillery units. 

KCNA said he warned against “all sorts of more frantic war preparation moves being committed by the enemy,” and called on his troops to be able “to overwhelmingly respond to and contain them all the time.” 

The North’s foreign ministry chimed in with a statement accusing the Americans of “scheming to coercively call an informal UN Security Council meeting to discuss the non-existent ‘human rights issue’ of the DPRK.”