As Iran is pummeled by Israeli air strikes, Tehran is counting on one final line of defense against the destruction of its nuclear program: the tunnels and bunkers in which it is hiding its resources.

The Israelis may destroy Iran’s above-ground sites, but North Korea masterminded construction of the underground complexes Tehran will need if it is to stave off defeat. In the end, American bunker-busting bombs will be needed to obliterate them.

“Nobody — nobody — builds underground facilities as well as the North Koreans,” according to one of America’s leading analysts of North Korea’s defenses, Bruce Bechtol. “So of course they built those facilities for Iran for a price” — cash and maybe oil.

The Israeli strikes provide what is undoubtedly the best test so far of the strength and depth of North Korea’s own underground defenses, developed to shield its nuclear program from attack in the event of a second war on the Korean peninsula. Using powerful imported drills and excavators, North Korea has gained invaluable experience testing and learning how to hide much of what it’s doing from the watchful eyes of spy satellites.

Bound in a de facto alliance that President George W. Bush labeled “an axis of evil,” Iran and North Korea both need defenses capable of withstanding hostile fire. The Israeli bombing of Iran provides lessons for the North Koreans, as their leader, Kim Jong-un, repeatedly tests his missiles while talking of the possibility of war during which his underground redoubts would be essential for hiding his nukes and missiles.

Going underground was vital in Iran’s nuclear collaboration with North Korea. “The project, estimated to have cost hundreds of millions of dollars, included the construction of 10,000 meters of underground halls for nuclear equipment connected by tunnels measuring hundreds of meters branching off from each hall,” an editor at the authoritative Jane’s Defense Weekly, Robin Hughes, writes. “Specifications reportedly called for reinforced concrete tunnel ceilings, walls, and doors resistant to explosions and penetrating munitions.”

The elite Islamic Revolutionary Guard Corps “drew on North Korean expertise,” according to a study by the Foreign Policy Research Institute, a think tank in Philadelphia, “in order to construct a defense infrastructure that would protect and conceal its military nuclear program.” Calling for “extensive tunneling and hardening projects” at nuclear sites at Natanz and Isfahan south of Tehran, the deal provided “on-site North Korean technical support” from one of the North’s top experts on underground facilities beginning in 2005.

Israeli warplanes have zeroed in on both of those sites and a number of others, including a much more fortified one at Fordow, closer to Tehran, whose caves and tunnels burrow so deep underground as to be inaccessible to conventional bombing. Undoubtedly the bombing has done considerable damage at all of the sites,  but the underground construction makes it impossible to assess the extent.

Much now depends on whether President Trump will agree to the use of bunker-busting bombs that are capable of blasting apart otherwise impervious complexes. Mr. Trump has said America did not participate in the Israeli bombing — so far. “It’s possible we could get involved,” he told an ABC interviewer, but he’s also said he thinks the war is “nearly over.”

If the war were to end now, one thing is sure: Iran would still have its missiles — and be able to revive its nuclear program.

 “Despite sustained Israeli airstrikes, Iran has managed to continue  launching ballistic missiles — a feat that can be attributed to the Islamic Republic’s long-standing military doctrine, decentralized infrastructure, and upgraded survivability tactics,” the Jerusalem Post said. “The Iranian Revolutionary Guard, have invested heavily in building an arsenal that would be difficult to neutralize in a single strike or campaign.”

With North Korea acting as a steady source of expertise and advice, Iran would be sure to remain a threat to Israel and the region just as the North threatens not only South Korea but the rest of northeast Asia.