by Farzin Nadimi  – PolicyWatch 3411 – December 29, 2020

Unusual deployments by the U.S. and Israeli navies may be intended to deter Iranian attacks in the Gulf, but both moves are ripe for misinterpretation in Tehran.

On December 21, the American nuclear-powered guided missile submarine USS Georgia (SSGN-729) transited the Strait of Hormuz and entered the shallow waters of the Persian Gulf. The massive vessel is one of only four in the U.S. Navy converted to carry 154 conventionally armed Tomahawk land-attack cruise missiles—about half the tactical missile strike capability of an entire naval task force, with ranges of 1,300 to 2,500 kilometers. The Georgia can also carry sixty-six SEAL commandos and deploy them covertly for clandestine operations. Offering robust intelligence gathering and task force command-level secure communications capabilities, the Navy’s four cruise missile submarines are usually assigned the most challenging tasks.

According to a December 22 statement from U.S. Central Command, the move demonstrates America’s “commitment to regional partners and maritime security with a full spectrum of capabilities to remain ready to defend against any threat at any time.” Ostensibly, it is a message of deterrence to leaders in Iran, warning them not to order attacks against U.S. personnel or assets in the region as the anniversary of Gen. Qasem Soleimani’s death approaches. Shortly after U.S. forces targeted and killed Soleimani last January 3, Iranian forces fired ballistic missiles at al-Asad Air Base in Iraq, causing material damage to U.S. facilities and injuring several American service members. Yet Supreme Leader Ali Khamenei and other officials continue to make public promises about avenging Soleimani, and the anniversary of the commander’s death coincides with a fraught U.S. presidential transition, raising fears that retaliation might come sooner rather than later.

Israel’s Move: Complementary or Coincidence?

On the same day that the Georgia entered the Gulf, Israeli media reported that an Israeli attack submarine had crossed the Suez Canal into the Red Sea in a very rare move, possibly heading for waters near Iran or even the Persian Gulf itself. The latter scenario cannot be entirely dismissed given the recent normalization of diplomatic and security relations between Israel, the United Arab Emirates, and Bahrain. Yet any overt Israeli attempt to transit the Strait of Hormuz would almost certainly lead to a faceoff with Iranian forces.

Israel’s advanced Dolphin II submarine can remain submerged for up to thirty days owing to its air independent propulsion (AIP). It can also reportedly carry cruise missiles with an unconfirmed range of about 1,500 kilometers, armed with conventional or nuclear warheads. In theory, then, the vessel could threaten inland targets near Iran’s coast while standing off in the Arabian Sea, or even the sensitive Natanz and Isfahan nuclear facilities if it risked sailing further north into the Gulf of Oman.

Israel chose to send its submarine through Suez, which requires surfaced transit, to avoid circumnavigating Africa. The journey’s timing may have been coordinated with the Georgia’s transit, but more likely not given the highly secretive nature of U.S. submarine operations. Another possibility is that Israel timed the move to coincide with the Iranian navy’s change of guard in the Gulf of Aden. Iran’s Task Force 70 had already returned home, and Task Force 71 had just set off on December 19 to take its place, leaving the Gulf of Aden and northern Arabian Sea without an active Iranian naval asset for a few days.

One of the stated duties of Iranian naval task forces is to monitor potentially hostile activities in these waterways and the Bab al-Mandab Strait. Composed of two main vessels—the frigate Alborz and the helicopter-carrying support ship Kharg (the largest vessel in Iran’s fleet)—Task Force 71 sailed from Bandar Abbas to the Gulf of Aden for anti-piracy and intelligence-gathering duties.

U.S. Naval Precedents and Risks

The U.S. Navy has a long tradition of not disclosing the whereabouts of its submarines, but Persian Gulf visits by nuclear-powered cruise missile subs (SSGN designation) are believed to be especially rare. The Navy’s smaller fast-attack submarines (SSN) frequently operate in the Gulf and are perfectly capable of conducting intelligence, surveillance, and reconnaissance (ISR) operations and other missions in the area. Yet the confined spaces of the Gulf and the Strait of Hormuz are believed to be inhospitable for large submarine operations because of their relatively shallow depths, strong currents, numerous underwater pipelines, offshore facilities, highly congested shipping routes, and modern detection technologies.

Indeed, the collision risks have proven to be significant. In January 2007, the Los Angeles-class attack submarine USS Newport News (SSN-750) struck a Japanese supertanker while leaving the Strait of Hormuz submerged. Two years later, the Los Angeles-class USS Hartford (SSN-768) collided with an amphibious support ship while conducting a submerged transit of the strait at night.

Iran’s Potential Countermeasures

The Islamic Republic of Iran Navy (IRIN) is believed to regard its three Russian-made Kilo-class submarines and its indigenous Fateh-class subs (both diesel-electric) as its first line of defense against enemy subs (the Saviz, an intelligence/armory ship permanently moored north of the Bab al-Mandab Strait, may play a role as well). When combining the resources of IRIN, the Islamic Revolutionary Guard Corps Navy (IRGCN), and its existing networks of sensors, Iran can detect suspicious submarine activities in nearby waters—especially in shallower depths that provide little or no thermoacoustic barriers (i.e., thermocline) for submarines to hide under. Meanwhile, Iran’s air defenses are capable of intercepting at least some of any cruise missiles fired at its sensitive facilities.

Besides deploying sonar-equipped submarines to locate submerged threats, Iran is also believed to have made small improvements to its anti-sub capabilities in recent years. These include a handful of S-61 (SH-3D) Sea King helicopters that can deploy tethered active-passive sonar and torpedoes. Iranian forces can also deploy bottom-laying anti-submarine mines in Persian Gulf littorals, while the IRGCN has a fleet of small torpedo speedboats (though their anti-submarine warfare capability remains unproven). On December 25, during a tour of fortifications near the Strait of Hormuz, IRGCN commander Alireza Tangsiri reiterated his outfit’s readiness to counter any threat.

Legal Aspects of Submarine Transits

The Georgia broke from normal U.S. naval practice in Hormuz by transiting the strait while surfaced and during daylight hours, escorted by two air defense guided missile cruisers and a spotter helicopter. There is a legal distinction between transiting an international strait while surfaced vs. submerged. The United States has insisted on the right of “transit passage” in Hormuz, a definition that allows for normal operations such as launching shipborne helicopters and keeping submarines submerged. Yet Iran does not consider Hormuz to be an international strait and therefore insists on the principle of “innocent passage,” which does not allow such operations.

In the past, the U.S. Navy frequently exercised its right to transit passage by sending submarines through Hormuz in submerged mode. Georgia’s surfaced transit was probably intended to appear more defiant and send a warning to Iran. Yet Tehran might interpret it as a sign of weakness—that is, a de facto capitulation to Iran’s longstanding insistence on “innocent passage.”


As Khamenei warned in a December 16 speech, Tehran is still bent on inflicting a blow painful enough to compel the ultimate departure of American forces from the Middle East. Therefore, the U.S. Defense Department has been taking steps to improve its local deterrent posture, such as maneuvering its only remaining carrier strike group in the region, ordering B-52 strategic bombers to fly directly from the United States to the Persian Gulf on December 10, and now sending one of its most versatile cruise missile submarines to the Gulf. Yet U.S. authorities need to be very careful in how they carry out such deterrent moves so that Iran does not misinterpret them as signs of weakness.

Moreover, in the unlikely event that Israel’s submarine approaches Iran’s waters, Tehran would probably react in dramatic fashion. Israel chose to forego any element of surprise by skipping the long voyage around Africa and sending its submarine through the Suez while surfaced, perhaps because it wanted a deterrent in the Arabian Sea sooner rather than later. Whatever the case, Iran will likely try various measures to dissuade the Israeli vessel from entering the Strait of Hormuz, such as declaring that this action would cross a redline, refusing the vessel the right of innocent passage, conducting military exercises in the area, and increasing its patrols to locate and interdict the sub. Although Tehran may stop short of actions that precipitate a shooting war, such confrontations would nevertheless carry substantial risk of escalation.

Farzin Nadimi is an associate fellow with The Washington Institute, specializing in the security and defense affairs of Iran and the Gulf region.
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