Iran has responded to the Trump Administration’s “maximum pressure” sanctions policy with a policy of maximum blackmail—defiantly escalating its nuclear efforts, stepping up attacks on Arab oil exports, and intensifying its proxy war against Israel. U.S. economic sanctions are powerful but slow-acting tools. As the cumulative effects mount, Tehran has become more aggressive in lashing out against U.S. allies, particularly Israel. To buy time for sanctions to work, prevent an Iranian nuclear breakout, and discourage attacks on American interests, Israel, or other allies, the U.S. needs to augment its deterrence of Iran by maintaining a favorable regional balance of power and strengthening U.S. allies against Iran.

The United States has deployed approximately 14,000 military personnel to the Persian Gulf since May to bolster the defenses of its Gulf Arab partners—and is reportedly considering the deployment of another 4,000 to 7,000 troops. Israel does not require U.S. troops, but it could greatly benefit from the transfer of specialized U.S. bunker-buster bombs that would give it the capability to destroy fortified underground targets, including key parts of Iran’s nuclear infrastructure, if necessary. Such a transfer would strengthen deterrence against Iran and give Tehran additional incentives to restart negotiations on the nuclear issue.

Iran’s Growing Aggressiveness

Since May 8, 2019, the first anniversary of the U.S. withdrawal from the Iran nuclear deal in May 2018, Iran has steadily escalated its pushback against U.S. sanctions by incrementally reducing its compliance with the agreement, formally known as the Joint Comprehensive Plan of Action (JCPOA). Tehran threatened to expand its violations of the accord every 60 days until sanctions are eased. In May, Iran announced that it would exceed the 300-kilogram cap on its enriched uranium stockpile. In July, it began enriching uranium to 4.5 percent, exceeding the 3.67 percent limit set by the JCPOA. In September it violated restrictions on research and development and began installing prohibited advanced centrifuges. In November, Iran began uranium-enrichment operations at the Fordow enrichment facility, a fortified underground site designed to produce enough enriched uranium for one to two nuclear weapons annually, according to Iranian nuclear documents stolen by Israel and revealed in 2018.

In addition to the nuclear front, Iran has escalated its destabilizing threats to regional security. Tehran developed a hybrid war strategy in which it has orchestrated covert and proxy attacks to obscure its responsibility, and, if only for a short time, to escape retaliation. Iran was behind mine attacks on tankers transporting Arab oil on May 12 and June 13 as well as the shoot-down of a U.S. Navy drone on June 20. After a pause, Tehran launched its boldest attack so far on September 14, targeting Saudi Arabia’s oil infrastructure in Abqaiq and Khurais with seven cruise missiles and 18 drones.

Iran also has entrenched itself in Syria and sought to tilt the regional balance of power against Israel by building up the rocket, missile, and drone arsenals of proxy groups such as Hezbollah, Palestinian Islamic Jihad, Hamas, and Iranian-controlled Shia militias deployed in Syria and Iraq. Israel has been targeted by more than 2,600 rockets launched by Palestinian terrorists from Gaza alone since March 2018.

To defeat Iran’s strategy of “fighting to the last Arab” against Israel, Jerusalem has undertaken a military campaign dubbed “the war between the wars.” It has quietly conducted hundreds of air strikes against Iranian and proxy military targets in Syria, Lebanon, and Iraq. Simmering tensions between Iran and Israel could swiftly erupt in a multi-front regional war.

U.S. Policy: Stronger Deterrence Needed

Iran’s increasing willingness to take risks to threaten U.S. interests and allies is a clear sign that deterrence is inadequate and needs to be bolstered. The Trump Administration has beefed up the U.S. military presence in the Gulf to deter and defend against Iranian threats, but the credibility of U.S. deterrence increasingly is at risk. The Trump Administration’s mixed signals on Syria, last-minute decision to abort a retaliatory strike for Iran’s downing of an American drone, and the Saudi–American failure to retaliate forcefully for Iran’s September attack on Saudi Arabia have dissipated the earlier deterrent effect of President Trump’s warnings to Iran. Iran does not doubt U.S. military capabilities—but has reason to question Washington’s willingness to use them.

On the other hand, Tehran has little reason to doubt Israel’s willingness to use force in defense of its interests. Israel has assertively challenged Iran’s efforts to exploit Syria’s civil war to establish a new front against Israel. Yet if the low-intensity “war between the wars” escalates into a full-fledged regional war, Israeli cities are likely to be bombarded by rockets, missiles, and drones launched by Iran’s Revolutionary Guards and terrorist proxies in Syria, Lebanon, Gaza, and possibly Iraq.

Jerusalem then will have little choice but to retaliate against military targets inside Iran—including facilities that pose a long-term existential threat to Israel. One of Iran’s most valuable strategic assets is the Fordow nuclear facility, but Israel currently has no means of destroying that fortified underground site short of using a nuclear weapon. Portions of the site are estimated to lie up to 300 feet underground, beyond the reach of Israel’s current military capabilities.

Recommendations

To bolster Israel’s ability to defend itself against Iran’s direct and proxy threats, the United States should:

• Strengthen Israeli missile defenses. The U.S. has stationed an American-manned X-band radar system in Israel and has temporarily deployed the Terminal High-Altitude Area Defense system, which includes the most advanced U.S. anti-ballistic missile technology. These actions, combined with Israeli deployment of the U.S.-made Patriot air defense system, along with its own Arrow, Iron Dome, and David’s Sling defense systems, have enabled Jerusalem to build a robust and layered defense against Iran’s increasingly sophisticated missiles.

  But Iran’s September attack on Saudi Arabia revealed its capacity to defeat air defenses through the employment of low-flying cruise missiles and drones. Washington should work with Jerusalem to develop and field more effective cruise missile and drone defense systems.

  However, Israel cannot defend against everything. Missile defenses can be overwhelmed by multiple salvos of incoming missiles. Israel therefore must go beyond deterrence-by-denial and focus more on deterrence-by-punishment—particularly by targeting assets that the clerical regime highly values.

• Explore the idea of selling Israel bunker-buster bombs to give it a military option that would boost deterrence. Israel’s air force could potentially benefit from acquiring the GBU-57 Massive Ordnance Penetrator (MOP), a U.S. Air Force precision-guided 30,000-pound bomb designed to pulverize deeply buried hard targets. MOPs have continually been improved, but by 2010 were capable of penetrating approximately 125 feet of moderately hard rock (or up to 200 feet of reinforced concrete), before detonating and generating an intense seismic shock wave to pulverize hardened underground targets. MOPs would give Israel options to destroy Fordow and other hardened underground sites that it currently lacks.

  Because its fighter-bombers are too small to carry MOPs, Israel also would require aircraft to deliver the weapon. The B-2 is the only aircraft currently capable of delivering MOPs operationally, although B-52 bombers have dropped some in tests. The Pentagon only has 20 B-2s and 58 B-52H bombers in active service (which it cannot spare), but it has 18 B-52H bombers in reserve, as well as 12 in long-term storage, that Israel could refurbish to deliver the MOPs.

  Israel may prefer to develop a less costly alternative to the B-52s, which in any case could not be delivered until after the expiration of the New START Treaty in February 2021. Israel’s air force, well-known for innovation as well as a higher tolerance for risk in military operations, is capable of coming up with imaginative solutions. But even if Jerusalem opts not to buy MOPs, the end result could help bolster deterrence because Tehran would be compelled to consider what alternative options Israel has developed that enable it to turn down the MOP offer.

• Strengthen other Israeli military capabilities to establish a more favorable balance of power. Washington should frontload delivery of arms under the $38 billion 10-year memorandum of understanding on military assistance. The Pentagon also should add to its prepositioned military stockpiles in Israel that could be transferred to Israel in a crisis, to upgrade the readiness and deterrence power of both countries.

Israeli MOPs Strengthen U.S. Diplomacy

Sanctions alone are unlikely to halt Iran’s nuclear program, just as they failed to halt North Korea’s. What is needed is firm diplomacy backed by the credible threat of the use of military force. Washington has focused on deterrence by denial, deploying additional military forces to the Gulf region. But Iran has developed innovative tactics to threaten U.S. allies.

Washington must defeat Iran’s strategy and restore deterrence to dissuade Tehran from its present course and force a return to nuclear negotiations. Tehran may doubt that the U.S. would attack Fordow, particularly if a Democrat opposed to Trump’s hardline policy is elected President in 2020.

But Iran is unlikely to doubt Israel’s willingness to strike. MOPs would strengthen Israel’s military capabilities, enhance deterrence of Iran, and encourage a negotiated resolution of the nuclear issue. Giving Israel MOPs would serve notice on Iran that its nuclear weapons program will be ended—one way or another.

James Phillips is Senior Research Fellow for Middle Eastern Affairs in the Douglas and Sarah Allison Center for Foreign Policy, of the Kathryn and Shelby Cullom Davis Institute for National Security and Foreign Policy, at The Heritage Foundation.