Could Iran shut the Strait of Hormuz, or significantly hinder traffic passing through it? A recent decision by the European Union to impose a total embargo on the purchase of Iranian oil has prompted threats from Tehran to close the world's most important oil chokepoint. However, an assessment of military capabilities deployed in the area, and of probable tactics, suggests that Iran would find it difficult or unpalatable to cause major disruption.
According to the United States Energy Information Administration, 17 million barrels of oil passed through the strait every day in 2011, or about 35% of all seaborne traded oil. Iran itself is heavily dependent on oil flowing through the strait: approximately 70% of the government's revenues come from oil exports, all of which currently transit the strait. Iran has no pipelines to its Indian Ocean ports or to countries to its east.
In late 2011 and early 2012, the Islamic Republic of Iran Navy and Iranian Revolutionary Guard Corps (IRGC) Navy conducted Velayat-90, a series of exercises that focused on sea denial. Although Iran possesses capabilities that could, at least temporarily, disrupt shipping, it seems unlikely that it would be able to close the strait for a prolonged period.
Iran's capabilities
Given the small size of its surface fleet, with just six corvettes of meagre capability, there is no possibility that Iran could, in the traditional manner, assert command of the sea in and around the strait. Therefore, rather than attempting to mount a blockade, Iran is likely to pursue a denial strategy to attack isolated or poorly defended ships.
Key weapons in such an approach would be mines, torpedoes, rockets and anti-ship missiles. To avoid direct conflict with American or other naval vessels in the region, Iranian forces would probably use submarines and fast attack craft to deliver weapons at sea, or flat-bed trucks to launch anti-ship missiles from land. Air-launched weapons could also be used, particularly as part of a combined arms operation, to provide a greater chance of success.
The sophisticated air defence capabilities of US and allied Arab forces in the region could deter Iran from regularly using its aircraft to launch strikes in the Gulf. Iran's air force does, however, have the capacity to mount strike operations using the Russian Sukhoi Su-24 Fencer, as well as the ageing F-4 Phantom. Work has been undertaken to integrate anti-ship missiles on the F-4, and it is conceivable that a similar effort has been made with the Fencer.
Such tactics would resemble the latter years of the 'Tanker War'. Lasting throughout the Iran-Iraq War of 1980-88, but with a significant escalation in 1984, this primarily involved the targeting of vessels carrying Iranian or Iraqi/Iraq-allied Arab oil and offshore platforms. According to a comprehensive CSIS study, 259 tankers and carriers were attacked between 1984 and 1988. Iraq's attacks consisted primarily of French-supplied Exocet missiles launched from fighter aircraft, particularly Mirage F-1s and Super Etendards, while Iran deployed a mix of helicopter-launched ordnance, anti-ship missiles (particularly the Chinese-manufactured Silkworm) and rockets, and a small number of mines.
The missile threat
Given the experience of the Tanker War and what is known about Iran's current capabilities, anti-ship missiles would be a significant consideration for US and allied forces. Iran's anti-ship missile inventory consists almost entirely of Chinese weapons. Supplies began in the mid-1980s and continued in spite of pressure from Washington on Beijing. Iran is thought to have initially received HY-1 (CSSC-2 Silkworm) and HY-2 (CSSC-3 Seersucker) anti-ship missiles. During the Tanker War it deployed coastal-defence variants of the CSSC-2/CSSC-3 in the Strait of Hormuz. In the 1990s, Iran acquired the C-801(CSS-N-4 Sardine) and the longer-range C-802 (CSSC-8 Saccade). These have been deployed on ships, and have also been vehicle-mounted for coastal defence. The C-802 is often referred to as Noor, though Tehran often reuses names for different systems.
Iran has also acquired at least three short-range missile systems from China. The Kosar family of weapons appears to include both the Chinese C-701 (Kosar 3 and Kosar 1) and the Hongdu JJ/TL-1 (Kosar), while the Nasr 1 and Nasr 2 correspond to the Chinese C-704. Like the C-801/C-802, the Kosar and Nasr are deployed on several platforms, including fast attack and patrol craft, and on trucks for coastal defence. Tehran may remain dependent on China for the provision of key components, although the Iranian media have shown pictures of final assembly lines and sub-components for the Kosar and Nasr.
Other missiles could also come into play. Iran claims to have tested the Ghader anti-ship missile during the Velayat-90 exercises. Based on the C-802 family - perhaps corresponding to the C-802A - this is a longer-range weapon fitted with a frequency-agile radar seeker to make the weapon less vulnerable to radar countermeasures. China has previously indicated that the range of the C-802A is 180km, compared to 120km for the C-802. By comparison, and according to Chinese brochure material, the C-701 has a notional maximum range of 25km, and the C-704 38km. Iran has also developed a version of the CSSC-2/CSSC-3 family, known as Ra'ad, using a turbojet rather than a solid-propellant motor to give a maximum range of more than 300km. It is not known whether Ra'ad has entered into service. In addition, work has been undertaken to integrate the C-801/C-802 on both fixed- and rotary-wing aircraft. Iran has also modified the Sea Killer/Marte Mk1 anti-ship missile with a TV seeker (sourced possibly from its stock of early-model US-made AGM-65 Maverick). This could provide an air-launched anti-ship weapon, but it is not known if it has entered into service in this role.
There is a diverse range of delivery systems for these weapons. Primary among them are small fast craft, such as the IRGC's 25 Peykaap II-class craft, which can reach speeds of more than 50 knots and carry two Kosar or Nasr missiles. While their range is limited by engine size and difficulties operating in rougher seas, they are highly effective littoral combatants. Because of their small size, they would not have to operate out of the Bandar-e-Abbas naval base on the Strait of Hormuz, but could use any available jetty. The Iranian-controlled islands in the strait (Abu Musa, Lesser Tunb and Greater Tunb - see map) also have naval facilities that could support such small vessels, for example. The use of several at any one time, using swarm tactics, could potentially allow them to reach a target in minutes before any nearby naval forces could react. They could launch enough missiles to sink a tanker in the strait. Larger but still fast patrol craft, such as the IRGC's ten Thondor-class patrol boats carrying the C-802 missile, or the Navy's 13 Kaman-class vessels with two to four Noor missiles, also provide a potentially lethal offensive capability, although their larger size makes them more vulnerable. Land-based launchers would further complicate defence against anti-ship missiles, as they can be placed anywhere along the coast and be moved after firing, making them difficult to locate and destroy.
Countering Iran's missiles
A campaign to strike tankers in the strait would be countered by a robust US and European naval presence. Various assets are readily available in the Gulf for such a response. Currently, the US Fifth Fleet, which is based in Bahrain, maintains a presence in the region of two carrier strike groups, an amphibious squadron, a mine countermeasures task force, a submarine task force and a logistics task force. The US Coast Guard also has six cutters in Bahrain, while US-led Combined Task Forces include assets from the UK, French and Saudi navies, among others. Though pre-emptive strikes against Iranian small craft in harbour could be attempted, the risk of escalation that this would carry suggests that a more likely response would be a convoy system to protect tankers and other commercial vessels.
The experience of the Tanker War suggests that such a system could be successful: the US Navy escorted 252 ships between July 1987 and December 1988, and during that period only one commercial vessel was damaged: the Bridgeton, a formerly Kuwaiti-flagged vessel that was reflagged as a US tanker, struck a mine during the first convoy, but continued under her own steam. British naval vessels conducted 1,026 transits in 1987 and 1988 as part of a convoy system. With an average of 14 very large crude carriers passing through the strait each day, a system involving ships of several nations escorting tankers in small groups two or three times a day seems a feasible approach.
Command and control of this or any other joint response could be a tricky political problem; it is unclear whether the Gulf Cooperation Council possesses sufficient capabilities to handle such a complex mission. Even if Washington is wary of assuming command, it seems likely that a command structure with strong US involvement could be forged.
The value of a convoy system would not just be in the missile defence offered by the layered missile-defence systems on board the US Navy's Ticonderoga-class cruisers and Arleigh Burke-class destroyers currently deployed with the Fifth Fleet. Standard SM-2 and Evolved Sea Sparrow air-defence missiles along with the Phalanx gun-based close-in-weapon system would provide the main tools to counter the air and missile threats.
However, were the Iranians to utilise swarm tactics with small boats bolstered by air- and land-launched missiles, it is possible that escort vessels would not be able to deal with all incoming ordnance in time. Escorting navies would hope that their presence alone would deter attacks in the strait - any Iranian attacks would, of course, offer justification for retributive strikes. As an indication, the only damage sustained by a US naval vessel in the Tanker War was to the USS Samuel B Roberts, which was struck by an Iranian mine in April 1988. This led to Operation Praying Mantis, an attack by two American surface groups on offshore platforms and a subsequent series of engagements that led to the sinking of an Iranian frigate, a Kaman-class patrol boat and three fast attack craft.
As well as missiles, torpedoes could also be used by Iran. Its fleet of 18 submarines (albeit 15 of them midget submarines) offers a useful undersea threat. To be able to launch an attack, however, a submarine would need to avoid detection by US and allied Arab forces' substantial anti-submarine warfare capabilities, a possibility in shallow waters but more difficult in the deeper waters of the Gulf.
Mining the strait
The laying of mines is perhaps the most effective method of disruption available to Iran, providing a means of closing the waterway while avoiding direct engagement with enemy forces. Mines are cheap weapons that can have a disproportionate effect: the Iranian M-08 mine that blew a hole in the hull of the USS Samuel B Roberts cost approximately $1,500 and caused $96m worth of damage.
The Iranian navy is estimated to have 2,000-3,000 mines, largely of Soviet or Chinese origin. They include moored and bottom mines, which could be activated both by contact and 'influence' (by sensing changes in the acoustic environment, magnetic field or water pressure, indicating a vessel's presence).To mine the entirety of the Strait of Hormuz effectively would take thousands of mines and several days. Iran could use Kilo-class submarines, which can carry 24 mines. But a larger operation would have to involve small craft and possibly commercial vessels. Though easily detectable, the laying of several hundred mines in a few hours could have a significant effect.
Mine countermeasures now available to the US and allied forces in the Gulf are far superior to those of the 1980s, when 176 mines were neutralised. The Fifth Fleet, for example, has four Avenger-class mine countermeasures vessels in Bahrain, and assets of the UK, French, Saudi and Emirati navies could also be called upon. Nonetheless, minesweeping/hunting is time-consuming: it may take days to open mine-free corridors, and weeks to clear the strait entirely. Escorts would not necessarily prevent mines from damaging commercial vessels travelling in convoy, as some mines can be programmed to detonate after the second or third vessel passes over them.
Mining may not, therefore, close the strait altogether, given the difficulty of laying enough mines in a short period. The mining of the Gulf in the 1980s did not prevent continued traffic. Nonetheless, the fear of a mine would deny large areas of the sea to traffic. For Tehran, this presents a problem in itself. Missile attacks have the benefit of being discriminatory and would, therefore, allow Iranian-flagged or -destined vessels to avoid attack. Mining the entire strait, however, would also close it to Iranian traffic, with the necessarily debilitating effects on Iran's ailing economy.
Other considerations
Two more options are open to Iran in any sea-denial strategy. The first is a small-craft explosive attack on a tanker, with the aim of sinking the vessel or causing a substantial oil spill, making an area impassable to shipping while it was being cleared. Such an operation would likely involve one or more small boats packed with explosives, most likely on a suicide mission, similar to the failed attack on the Japanese tanker M Star in July 2010. But the operational challenge of manoeuvring a small boat packed with up to 1,000kg of explosives close enough to a tanker to penetrate two hulls is self-evident.
A second option open to Tehran would be not to target the Strait of Hormuz itself but to hit shipping further up the Gulf, as occurred in the Tanker War. With this approach, it could be easier to avoid confrontation with US or other navies, which could be concentrated around the strait. Vessels at anchor in the Gulf would be most vulnerable. Operations would not have the dramatic effect of attacks in the strait, but could be easier to accomplish.
Though facing vastly superior military capabilities, Iran has a number of military options in the Gulf. While it may not be able to carry out its threat to 'close' the strait, it could cause significant disruption to shipping - and also invite a hostile response.