Iran wields Hormuz threat

16 July 2018
10th July 2018, Week 27, Issue 638

While Tehran’s recent threat to close the Strait of Hormuz should be taken with a pinch of salt, NewsBase Research (NBR) has taken a closer look at the conditions surrounding such a closure

What: Should Iran close the Strait of Hormuz more than 18 million bpd of crude would stop flowing from the Middle East.

Why: The Iranian government’s threat comes in response to the US’ planned resumption of sanctions.

What Next: Any such closure of the strait risks boiling over into a wider confrontation within the Persian Gulf.

One of Iran’s responses to the imminent demise of Joint Comprehensive Plan of Action (JCPOA) was to make a somewhat intemperate threat last week to “close Hormuz”. That is a phrase easily bandied about, as if the Strait of Hormuz were another Suez Canal, closed as easily as a door. Is Iran’s threat real, or empty?

In 2012, the last time tension in the Persian Gulf was high enough to put Hormuz on the risk agenda, NewsBase Research (NBR) carried out an extensive analysis of a possible Hormuz closure.

This was based on detailed wargaming (with technical and tactical input from military authors current enough to be useful), a detailed analysis of the politics, international law and behavioural aspects of a closure, and our guiding tropes of Hard Data and Cold Logic. The result was a 30,000-word study delivered in six briefings. A seventh, eighth and ninth briefing – covering oil prices, the extension of a Hormuz war into the Gulf, and what would happen afterwards – were cancelled when peace broke out towards the end of 2012.

NBR’s work certainly found an audience – 5,000 of our customers downloaded each of those six briefings. It is probably too soon to go back over these grounds and update the briefing in depth – President Hassan Rouhani’s threat does not appear to have been intended seriously, despite China taking the unusual move to reproach Tehran over the warning – but now is probably a good time to rehearse some of the governing circumstances that apply to this issue in order to lay a few myths to rest and to show some of the bounding conditions that would apply to a Hormuz closure.

Spatial awareness

First, the water-space. Hormuz is usually presented by the commentariat as a narrow, constricted space in which a small quantity of force can obtain a dominant effect. It is not. At its narrowest Hormuz is around 60-km wide. It is also some 200-km long.

Iran only has to close Hormuz at one point, while its opponents have to keep a long channel open at all points. Iran can probably dominate the northern edge of Hormuz using sea-skimming missiles, but cannot effectively dominate, or even target, traffic which hugs the UAE and Omani coasts with guided weapons.

While the Traffic Separation Scheme currently takes tanker traffic in a wide arc around the northern edge of Hormuz, that is for convenience and not because of any lack of water space. Tankers under more active (war-fighting) control would hug the southern edge of Hormuz. This would put them out of reach of most surface-to-surface missile (SSM) attack – but not all, see below.

An important feature of a Hormuz war is that attacks on civilian shipping are strictly contrary to International Law. Iran’s PR image portrays it as a state indifferent to International Law, but Tehran is likely to pay rather more attention to it than the commentariat expects. Iran has only breached international law once, during the 1979-81 hostage crisis, with everything done since the revolution being in compliance.Based on that assumption then missile attacks on tankers seem to be unlikely.

Iran’s strategy for closing Hormuz is more likely to rest mainly on the use of mine warfare. Most of Hormuz is shallow enough to make practical use of sea-bed mines – known as ground mines, in contrast with moored mines, which float tethered to a sinker. There is one deep channel at the tip of Oman, off the Mussandam Peninsula, which is probably too deep for ground mines to work effectively, and that is where the war-channel would go. But the channel’s approaches on both sides are shallow enough for mining, as are the waters between it and Iran, where a warship screen would have to operate.

If it set out to close/control Hormuz, Iran would begin by using its flotilla of small submarines to lay ground mines in advance of a declaration of closure. This is why these boats have been built and they are perfectly tailored to their task. The mine-lay would stop all tanker traffic through Hormuz immediately, stranding a dozen or so tankers in mid channel as a side effect.

Opening Hormuz then becomes a mine-clearance task, through the use of minehunters, drones and helicopter minehunters.


Minehunters are small, slow, unprotected ships of 500-1,000 tonnes. On task they creep slowly from clear water to mined water, searching the sea-bed with high-resolution sonar. A good image to hold is a person using a laser pointer at night to find a squash ball in Central Park.

In order to operate a minehunter, which is defenceless, there must be effective three-dimensional cover against threats from air, surface and sub-surface attacks. While the Allies – the GCC, NATO and probably India – may rely on winning air superiority very quickly, surface and sub-surface superiority will take much longer to achieve. Other minehunting solutions are either very new and untried (drones) or partially effective (minehunting helicopters). A very substantial effort would be required to clear a swept channel.

As the scale of the Allied effort grew it would be essential for the Allies to build a functional coalition that would need legal authorisation from the UN, which would take time, and the reconciliation of many competing agendas, taking even more time. The Alliance would have to include the US, NATO, the GCC, Egypt, Israel (probably), a collection of ASEAN states, Japan and Qatar (probably, again), and it would have to negotiate its way past Iran’s allies and supporters, principally Russia and China. The process of Alliance-building would take time, as it would catalyse a plethora of competing side-agendas, deals and paranoias, and in many cases would need national parliamentary authority. “Messy” is probably not the right word, but “slow” is.

Having carried out its initial mine-lay, Iran would work to “top-up” its minefields, while attacking Allied mine-clearance assets. New mines would be laid by submarine and from small fast boats, which can transit from Iran to the southern strait and back overnight. The Allies would succeed in sinking the submarine flotilla eventually, but that task will take much longer than hoped since the water and sonic conditions of Hormuz do not favour anti-submarine warfare (ASW). Most Iranian boats will be sunk at their berths. ASW will also be hampered by the fact that Allied surface ships will not be able to operate in the northern arc of Hormuz because of the surface missile threat.

Swarm tactics

Small-boat swarms of 20-100 units will periodically re-lay mines in cleared water. While large warships are now reliably capable of protecting themselves against attack by small craft they are not capable of preventing small craft from entering a wider area more than a kilometre or two away. In any case Allied warships will not enter mined waters until they have been cleared.

Thus, the only practical way of disrupting a small-craft swarm attack on the swept channel, which might arrive from three of the four points of the compass, is by the use of attack helicopters, large drones and ground attack aircraft, all armed with light ground attack missiles. Attack helicopters would also find success with their chain guns.

In this contest the balance of advantage will lie heavily with Iran.

Swarm mining attacks by small fast craft (a small RIB is sufficient) can be launched at short notice from a 180-degree arc of Iranian coastline 250-km long, offering a 60-120 minute transit time from Iran to the swept channel. That means attacks can take place at night, greatly hampering defence, and it also means that the defending force must persist in strength over the target zone 24/7, placing intense burdens on even a large Allied force.

The challenge is intensified by Hormuz’s atmospheric conditions. High air temperatures reduce aircraft payload and endurance, dust wears turbines and gears, and haze makes target acquisition hard. It is worth noting here that Hormuz is 160 km from the “easy” bases for Allied air cover, a distance that materially undercuts rotary time on task.

As Iranian small craft are destroyed by the defending screen their wreckage will form a debris-field on the seabed that multiplies the mine-clearance task by one or two orders of magnitude. Every piece of debris in the swept channel will have to be charted and classified as a mine or non-mine, including the cheap mine-like reflectors scattered in numbers from every attacking swarm craft.

Time management

The mine-clearance task cannot even begin until the Allies have established surface and sub-surface dominance over the southern arc of Hormuz.

Surface assets will be unable to enter the battlespace until enough water for them to operate in has been declared mine-free, turning this process into a painfully slow game of leapfrog in which mine countermeasure (MCM) assets delicately lead major warships into mined waters in order to clear sectors for those warships so they in turn can provide cover for the minehunters. The Allies would eventually succeed, but the process would take months.

Adding to these delays, the dozen or so minehunters pre-deployed to the Gulf and operated by the UK, the US and the GCC will be entirely inadequate to the task. To dive into detail, a well-handled minehunter might clear 0.25 square km per hour of seabed with a low level of debris. The Hormuz tanker route, starting around Abu Dhabi in the west and ending around Fujairah outside Hormuz, will require around 500 square km of swept channel (500 km by 1 km).

MCM drones are now bringing added resource but are few, untried in conflict and require surface vessel support. Therefore, substantial additional MCM assets would have to be deployed. Deployment of MCM ships – mostly from north European waters – is likely to be painfully slow and only made marginally less so by the use of shiplifts.

Deployment of MCM helicopters, favoured by the US Navy – is faster, but the technology has yet to be proved in an active conflict, is not optimised for ground mines, is undercut by atmospheric conditions as helicopter endurance falls and equipment is degraded by sand, and the Sea Dragon helicopters themselves are already at the end of their operational life. While minehunting skills in those dozen ships are well-honed and regularly exercised, the numbers are not on their side.

We should therefore expect a period in which MCM assets are slowly gathered from around the world and then more slowly pushed forward into a contested battlespace in which the rate of mine-laying will probably exceed the rate of mine-clearance.

A single declared mine in the swept channel will stop tanker traffic from using it. During this contest minehunters themselves will come under attack from small craft in the minelaying swarm equipped with rockets, man-portable missiles and heavy machine guns. Minehunters are more or less defenceless from attacks of this kind, have no armour and their operations can be stopped with even trivial levels of damage. The Allies should expect to lose many.

Managing chokepoints

Iran is likely to close only the southern and central parts of Hormuz, keeping a clear tanker channel close to its own littoral for the passage of tankers with flags and/or customers acceptable to Iran.

This in practice means tankers flagged to China or carrying China-owned cargoes. It might also include tankers flagged to Pakistan, India and other states outside the Alliance. It may even include tankers flagged to Allied states, presenting the Allies with the intriguing problem of whether to allow oil and gas to be shipped in this way or to interdict and arrest their own supplies and tankers in order to apply pressure to Iran.

Iran would prevent unauthorised tanker traffic from using its clear channel by boarding tankers that infringed its permissions. As the Allies-protected tankers try to use the inshore channel Iran is likely to activate “command” mine-fields to stop unauthorised traffic. The Allies might well end up mining the Iranian channel using nuclear submarines, though that would make the Hormuz oil crisis more intense.

Eventually, after many months of force build-up and attrition, the Allies would take effective control of the southern Hormuz battlespace in all three dimensions – surface, sub-surface and air – to create a narrow, single-lane tanker channel for tidal operation. This will mark the practical end of the Hormuz blockade. But even after this point Iran will retain some options.

Iran’s options

One option would be the use of SSMs fired into the tanker channel. Here geography and atmospherics favour the Allies – the southern arc of Hormuz is at the limit of Iranian subsonic SSM ranges. All SSMs would require recent accurate targeting data, which will not be easily obtained since the target would be well over the horizon and air surveillance will not be available.

A significant “unknown” – at least to the public domain – is whether Iran has a stock of the Russian-made Mosquito SS-N-22 (Moskit) missiles. Moskit is a sea-skimming missile that operates at some four times the speed of a traditional subsonic SSMs – think Exocet – and carries twice the payload. Moskit’s speed and cruise height give its target only 20 seconds in which to react once Moskit appears over the horizon. This speed also makes targeting easier, as very short flight times make short-life intelligence usable. This means that a single small craft could provide sufficient real-time-targeting data to allow a successful Moskit salvo to be fired into the swept channel at the covering warships.

Moskit, therefore, presents a new order of threat to both tankers and their warship screen. If Iran has Moskit then the Allies might find it impossible to obtain the surface domination they need to sustain mine-clearance.

A second Iranian option would be to escalate the Hormuz war into the Gulf proper. With a littoral of 700 km and a plethora of wells, platforms, terminals and channels it is probably not possible to predict with any useful degree of confidence how that conflict would play out. Some governing circumstances are clear.

With a 700-km littoral and only 150 km of water between Iran and its potential targets the question of who would control the battlespace is more open. A “full-Gulf” conflict is likely to result in tanker traffic on both sides using routes as close as possible to their respective littorals. Iranian threats to the Gulf would spread Allied resources over a much wider area, reducing cover for the Hormuz swept channel and so might permit a re-run of the Hormuz mining campaign.

Limited upside

One major class of Allied asset that would probably play a small, or no, part in a Hormuz blockade – the Carrier Strike Group (CSG). The US is likely to insist that any deployed CSG keeps out of range of Iranian SSMs launched from the southern littoral into the Gulf of Oman.

At the same time, in order to be within useful reach of Hormuz – near enough to launch sorties with a useful combination of weapon load and loiter-time – the CSG would have to operate somewhere west of Muscat. These conditions combine to force a CSG to operate in a small, 150 km by 50 km oblong shaped area to the northwest of Muscat. Over time, with an average force speed advance of 25 knots (46 kmph) and covering 15 km of water in every direction, the CSG would effectively cover all of the water in that oblong several times each week.

Iran’s tacticians would be likely to deploy one of Iran’s handful of ocean-going submarines into this small operating “box” to wait for the CSG to pass within strike range, around 5 km. Iran’s large submarines are of the Russian-built Kilo class, equipped with Air-Independent Propulsion (AIP). The Kilo is now known in the submarine trade as “the black hole” – being almost impossible to detect. The threat is real and acknowledged by naval planners.

In 2005, the Swedish AIP diesel-electric boat Gotland carried out multiple attacks on USS Ronald Reagan in task force exercises. Staffs deemed these attacks successful. Other more recent exercises have had similar results.

Apart from being highly vulnerable, the physics of deck-launches in hot temperatures make a CSG a very elaborate and risky way of generating a small quantity of force over Hormuz.


NBR’s 2012 study showed that a Hormuz war would not be over quickly and that forcing the strait open in face of Iranian opposition would require most of the Allies’ available front-line forces in the form of attack helicopters, major warships, strike aircraft and minehunting assets. It would take several months to achieve, in addition to whatever time was required to form a functional Alliance in the first place. The concept favoured by the commentariat – of a swift and overwhelming application of US force to open Hormuz – bears no relation to reality.

Little has changed in the forces available since 2012. Drone minehunting has made some steps forward, but mostly in shallow coastal waters and good conditions. US airborne MCM capability has aged and degraded. Most other technologies and assets have seen no change, except in a steady diminution of numbers. A Hormuz closure would not be a slam-dunk for NATO or the GCC, but a hard and painful asymmetric slog.

While the strategic conclusions from 2012 still appear to be valid, lack of time has prevented NBR from conducting a full Dynamic Iterative Forecast (DIF) of how a Hormuz blockade would affect oil and LNG prices. We may revisit that DIF in future if the political temperature rises high enough to justify the resources.

Edited by

Ian Simm


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