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The 30,000-pound Massive Ordinance Penetrator (MOP) is the largest bomb in the U.S. arsenal, and its new design is tailored specifically for striking Iran’s Fordow nuclear enrichment complex. Adam Entous and Julian Barnes at The Wall Street Journal (WSJ) report that not only has the MOP been refined for an Iranian strike, but it’s also being used to assure Israel the U.S. can keep Tehran from acquiring a nuclear bomb.

MOP Illustration, Boeing

In recent weeks, American officials, seeking to demonstrate U.S. capabilities, showed Israeli military and civilian leaders footage of a secret Air Force video of an earlier version of the bomb hitting its target in high-altitude testing. They also explained all the improvements the bomb underwent, this according to diplomats who were present.

According to Business Insider Australia, in the video, the weapon can be seen penetrating the ground within inches of its target, followed by a large underground detonation.

The upgrades include “adjusted fuses to maximize its burrowing power, upgraded guidance systems to improve its precision, and high-tech equipment intended to allow it to evade Iranian air defenses … [as well as] capabilities designed to counter Iran’s air defenses and keep the bomb on target if the Iranians try to knock it off course.”

Initial modification of the MOP was announced in January when the Pentagon’s director of operational testing, Michael Gilmore, confirmed that tests conducted with the heavy GBU-57 MOP GPS-guided bomb, thought able to penetrate 200 feet of concrete before exploding, had demonstrated it was able to hit and destroy deeply buried targets.

The enhanced MOP features tail-fin modifications to fix bugs identified in tests as well as a second fuse to destroy hardened underground targets. Gilmore said that the modifications were tested with five bomb drops from a B-2 stealth bomber on the White Sands Missile Range, conducted between June and October, and two ground tests. The WSJ article says the Iranian tailored MOP has yet to be dropped from an aircraft.

Hopefully we never have to use it,” a senior U.S. official also told the WSJ. “But if we had to, it would work.”

The U.S. hopes the new MOP, and its ability to inflict significant damage on Iran, will keep Israel from launching a unilateral strike against Tehran in the near future.