Closing Time: Assessing the Iranian Threat to the Strait of Hormuz
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Iranian closure of the Strait of Hormuz tops the list of global energy security nightmares. Roughly 90 percent of all Persian Gulf oil leaves the region on tankers that must pass through this narrow waterway opposite the Iranian coast, and land pipelines do not provide sufficient alternative export routes. Extended closure of the strait would remove roughly a quarter of the world’s oil from the market, causing a supply shock of the type not seen since the glory days of OPEC. Even if the strait were not closed in the sense of being physically barricaded, military conflict in the area could cause prices to skyrocket in anticipation of a supply disruption—and to remain high until markets could be assured that the flow of commerce had been restored. Consider that when Iraq invaded Kuwait in 1990, temporarily halting the export of oil in both countries, the world price of oil more than doubled merely on the expectation of future shortages. Although excess global supply combined with increased Saudi production helped lower the price within a few months, it did not return to the preinvasion level for nearly a year. Blockage of the strait would pose a vastly greater threat to the flow of gulf oil, and at a time when excess global capacity is lower and the price of oil higher.
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If the United States or Israel attacked Iran, the restraint that previously characterized Iranian behavior in the strait might evaporate. Indeed, in 2006 Iran’s supreme leader, Ayatollah Ali Khamenei, cautioned that although Iran would not be “the initiator of war,” if the United States punished or attacked Iran, then “definitely the shipment of energy from this region will be seriously jeopardized.” The Iranian oil minister made similar comments, hinting that “if the country’s interests are attacked, we will use all our capabilities, and oil is one of them.” One can imagine other events that could bring Iran to the same point of desperation—for example, if it were losing a conventional war with any of its neighbors and wanted to open another front as a punitive measure or a distraction. Short of the extreme case in which the United States preemptively destroys much of Iran’s military, there is an intermediate range of scenarios in which Iran is deeply threatened yet parts of its military are still intact and functioning. It is in this context that threats to block the strait could become reality.
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It would be challenging, though not impossible, for Iran to use its submarines for mine laying in the strait, due to several factors. First, the underwater geography of the strait neutralizes many of the characteristic advantages of submarines. Kilos require a minimum operating depth of 45 meters, and only in a few places is the water in the strait more than 80 meters deep, limiting the use of tactics such as diving for concealment or protection. Additionally, the high salt content of gulf waters and other factors create heat currents that disturb sonar. As a result, it is harder for submarines to use passive sonar to detect ships without revealing their own location. Submarines become hidden but irrelevant platforms, or useful platforms that are easier to find. Either way, antisubmarine warfare forces gain an advantage, and U.S. ASW patrols in the gulf would be likely to detect mine-laying activity by Iranian submarines. There is evidence Iran may have realized these problems and is planning to relocate its submarines to the Gulf of Oman.
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Iran is believed to possess at least 2,000 mines. By historical standards, this is not a large stockpile. For example, the British and Americans laid more than 70,000 mines in an effort to seal the North Sea against German U-boats in World War I, and the United States and the Soviet Union each stockpiled hundreds of thousands of mines during the Cold War. Nevertheless, even small numbers of mines have been able to halt surface traffic when their presence was known. In 1972 the United States immediately stopped all traffic in and out of North Vietnam’s Haiphong Harbor with an initial drop of only 36 acoustic-magnetic mines. In 1991 the Iraqis were able to discourage a U.S. amphibious invasion by laying only 1,000 mines off the Kuwaiti coast, 2 of which later hit but did not sink U.S. warships. In 1950 the North Koreans delayed the U.S. landing at Wonsan by laying only 3,000 mines across 50 square miles. As these examples show, mines derive much of their power from the fear they induce, which is often based more on the psychological effect of a lucky initial explosion than on rational calculations of risk.
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The general point is that it does not require great imagination to think Iran could lay several hundred mines in the gulf. If the above conditions prevailed, for example, Iran could lay a total of 693 mines. This is not an especially large number, but in such a conªned area with such heavy commercial traffic, it would not take long for a tanker to encounter a mine. The effects of the MDM-6 mine on a tanker are unknown, but given that these mines have both more sophisticated detonation mechanisms and ten times the charge of the mines that hobbled tankers in the 1980s, the threat to tanker traffic cannot be dismissed easily. If shipping companies—and their insurers—believed that large swaths of the channels and surrounding areas were deªnitely mined, and in some places with mines ten times as powerful as what was seen in the tankers wars, they likely would halt or reduce shipping. Most important, however, an Iranian mine warfare campaign against shipping would guarantee U.S. intervention, fulfilling Iran’s basic goal. The common assertion that 2,000 to 3,000 mines would be needed to close the strait may not take this potential Iranian objective into account.
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Iran’s limitations, such as the command and control and targeting challenges it would face in littoral warfare, are not often appreciated. But its strengths are often overlooked as well, such as the stocks of missiles and much more explosively powerful mines it has acquired since the tanker wars of the 1980s. Likewise, although the United States retains the world’s best conventional military, its past experiences hunting mobile targets from the air and conducting MCM operations in the littorals do not inspire confidence that confrontation in the strait would end quickly. The United States’ fleet defenses have never been tested in combat against an adversary with large numbers of cruise missiles, and the United States is in the midst of a major transition in its entire concept of MCM operations. Given these realities, sanguine assurances about the course and outcome of military conflict in the strait seem unjustified at best, and dangerous at worst. Most important, Iran does not have to seal the strait entirely to provoke U.S. intervention, and once that intervention begins, the potential for further military escalation is high. In particular, if the air and naval campaigns appear to be dragging on, the United States might be forced to consider holding hostage other targets in Iran or using ground forces. Either way, a significant and sustained increase in the price of oil would seem likely.
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Above all, the scenario described here points to the critical importance of early detection of any Iranian mine laying in the Persian Gulf and especially the need to keep close tabs on Iranian submarine activity. Such surveillance depends not only on U.S. activities in the region but also on those of Iran’s gulf neighbors. If the United States wishes to continue to act as the guarantor of free passage in the strait, it needs to make these monitoring activities a clear part of a broader effort to discourage Iranian attempts at harassment or closure. It also may wish to convey to Iran that, precisely because of the potential length and complexity of the operations outlined in this article, a campaign to clear the Persian Gulf of Iranian mines could quickly become a war to clear the Iranian harbors and coast of most remnants of the country’s military.