Securing The Red Sea

On 30 December the USS Gravely, an Arleigh-Burke-class destroyer, responded to a distress call from the Maersk Hangzhou along with the USS Laboon. The CENTCOM post on X noting the event states simply that Gravely shot down two anti-ship ballistic missiles (ASBMs) in the process of responding. An ASBM is technically a significant maritime strike capability; the fact that a non-state actor is in possession of this kind of weapon, and is employing it with impunity, is of grave concern. The US and its partners have responded to these attacks – 25 in total between 19 November and 4 January – primarily with defensive methods. However, a 4 January statement from the White House promised “consequences” if the Houthis do not end their attacks. This article will examine the Houthis’ capabilities and targeting possibilities for Western partners to counter them, as well as the difficulties they might face in doing so.

Top-Shelf Capabilities

The Houthis are able to deploy a range of missiles, drones and uncrewed kamikaze boats. Theoretically, the most sophisticated weapon available to them is the Asef ASBM, which carries a 500 kg warhead and has a range of 400 km. It employs an electro-optical seeker for the terminal phase of its target engagement, and is believed to be based on the Iranian Kahlij Fars ASBM. The Houthis also have access to anti-ship cruise missiles (ASCMs) such as the Al-Mandeb 2, which appears to be a close copy of the C-802, a Chinese ASCM sold to Iran in the 1990s. It has a range of 120 km and a 165 kg warhead; Iran reverse-engineered the C-802 into a domestic variant known as Noor. The ASCMs are truck-launched and have been used by the Houthis to damage and attack multiple ships since 2016. The C-802 or Noor was also used by Hizbullah to damage the Israeli ship INS Hanit in 2006.

The Al-Mandeb 2 and Asef represent just two of the anti-ship missiles available to the Houthis; they claim to have developed many more domestically. The US disputes this claim and has reiterated that Iran either provides the weapons, or is instrumental in enabling the Houthis to build them. In addition to their arsenal of anti-ship missiles, the Houthis are also able to employ uncrewed aerial vehicles (UAVs) such as the Samad-2 and -3. The latter can travel more than 1,500 km with an explosive payload, and is equipped with a dorsal antenna which likely enables it to be remotely operated as it approaches its target, while possibly being controlled in its terminal phase by a nearby operator on a small boat or onshore (though some UAVs may be controlled using satellite communications). Furthermore, the Houthis have attempted to board and seize vessels, as well as attack them with suicide boats.

Strengths and Weaknesses

The primary strength of the Houthi missile arsenal is experience. The Saudi Air Force has been conducting strikes in Yemen since 2015, which means the Houthis have become adept at minimising the damage that they cause. In 2018, for example, they unveiled an underground missile launcher that was designed to conceal the launch site of ballistic missiles fired into Saudi Arabia. The Saudis were initially able to destroy much of the original Houthi missile arsenal in 2017, which was inherited from the Yemeni military. However, since then, the Houthis and Iran have developed and manufactured many more missiles and drones – 70 were fired into Saudi Arabia in March 2021 alone, with a total of 340 launches that year, despite 600 Coalition airstrikes per month. Not all of those airstrikes were targeted at the Houthi missile production infrastructure, but the number nevertheless serves to illustrate the group’s familiarity with Western air power.

The crucial weakness of the Houthis’ maritime strike capabilities is their lack of effective targeting infrastructure. A series of coastal radars were used in 2016 to coordinate attacks against UAE and US vessels in the Red Sea. However, three of them were subsequently destroyed by US strikes, and it is unlikely that the Houthis would use the same tactics again. Instead, it is believed that they are provided with intelligence from an Iranian surveillance ship, the MV Behshad. The Behshad is thought to be limited in its intelligence-gathering capabilities to signal intelligence (SIGINT) and observation of shipping movements. Its predecessor vessel, the Saviz, which was also a converted civilian cargo ship, carried a complement of fast boats which could be used to provide visual identification of target vessels as well as SIGINT. This, coupled with data UAVs and open source AIS tracking, can be used to triangulate the range and bearing of a target vessel.

Securing shipping requires a disproportionately resource-intensive effort on the part of the defender relative to the attacker when the latter has the advantage of proximity

This would be sufficient to fire an ASCM in the direction of a vessel, while relying on its onboard seeker to identify a target in the terminal phase. This form of targeting would be less effective against warships, which can take evasive action and deploy countermeasures, but it is sufficient to enable strikes on commercial vessels. In principle, this should also be a viable means of targeting ASBMs, particularly as the altitudes that these missiles reach mean that their onboard sensors can cover very wide areas in the terminal phase. The challenge, however, is that ballistic missiles require a manoeuvrable re-entry vehicle (MARV) to be accurate against moving targets. MARVs are inherently difficult to design and could not be easily moved from Iran, so it is not clear that Houthi ASBMs have them. This could explain the margins by which they appear to have missed their targets.

The Challenges of Defence and Coercion

A major issue facing the Coalition is not the difficulty of intercepting Houthi missiles and UAVs per se, but rather the cost of doing so and the mismatch between tactical and strategic effectiveness. While vessels such as the USS Carney have proven highly capable, they have had to expend disproportionately expensive interceptors such as the SM-2 and ESSM in order to engage relatively cheap targets. Moreover, the challenges of replenishing vertical launch cells at sea mean that once a destroyer has expended its missile magazine, it must rotate to a friendly facility to reload. Aircraft such as the carrier-based F/A-18 can operate in a defensive role and can be reloaded more effectively, but this requires the persistent presence of a US aircraft carrier in the region when the demand signal from other theatres is growing.

Overall, securing shipping requires a disproportionately resource-intensive effort on the part of the defender relative to the attacker when the latter has the advantage of proximity. This was illustrated during previous challenges to freedom of navigation such as the 1980s Tanker War. Because of this, the Coalition may have to shift its approach from defence to coercion, as only a cessation of Houthi attacks is likely to mitigate the effects of increased insurance costs and lengthened shipping routes. The challenge will be identifying an appropriate approach, as the Coalition will have to balance the need to present the Houthis with a credible threat to compel a change in behaviour with preventing misperceptions by both the Houthis and their Iranian backers which could lead to a larger conflict. Faced with the rollback of Hamas in Gaza and the possibility of an Israeli attack on Hizbullah, the Iranians could misperceive an extensive strike campaign against the Houthis as being part of a broader effort to roll back their regional proxy network, and may react unpredictably.

Three Possible Approaches

One approach, dubbed “turning the screw”, involves limited actions with the threat of more to come. This approach entails striking a target of marginal value, such as a missile launcher or a coastal radar, while withholding the option of further action to give the target an opportunity to comply. Though the Houthis have become adept at operating under conditions of adversary air superiority, countries such as the UAE have struck Houthi missile launchers in the past, and the US struck Houthi radars in 2016 in a similar effort. However, this approach cedes the option of escalation to the opponent, who may perceive limited action as evidence of irresolution and continue as if nothing had happened. This leaves the options of further strikes or backing down, and could mean sleepwalking into the large-scale conflagration one is trying to avoid. Should initial failure result in wider strikes to disable a larger number of launchers, this might prove indistinguishable from a full-scale bombing campaign to the Iranians.

An alternative approach would be to present the Houthis and Iranians with the prospect of large-scale attacks on the Houthis’ military infrastructure, along with a privately communicated deadline for compliance. Posturing for action at scale while communicating the conditions for de-escalation can deliver effects, as it did during the 1996 Taiwan Strait Crisis, but time is on the side of the opponent. Posturing the resources needed to act at scale can only be done for a limited period, and an opponent can always desist for a time and wait for aircraft carriers to rotate out before resuming attacks. However, such an approach could secure temporary relief.

The Houthis are a persistent and determined opponent, and it is unlikely that they will halt their strikes simply because they are ineffective

The most viable coercive approach would likely involve direct attacks against a limited but valuable target set. The model here would be Operation Praying Mantis, in which the US Navy sank a portion of the Iranian fleet during the Tanker War, but desisted from carrying out strikes inland. The target set chosen was valuable enough to dispel any ambiguity about irresolution, but did not threaten the Iranians with the prospect of wider US attacks.

Any target set chosen must combine several characteristics. It should involve targets with concentrated value where sufficient damage can be inflicted with a minimal number of strikes. It should also involve targets related to the Houthi maritime strike capability and exclude assets that are not, in order to signal limited intent. The latter would include command and control nodes, as strikes on them could be viewed as the opening stages of a wider campaign. There are targets within Yemen which might meet this description. For example, the Houthis’ indigenous missile manufacturing capability might represent a target that can be struck on a limited basis. Though the Houthis import missile components, assembly is often done locally and thus requires some specialist equipment and personnel, with the latter being especially hard to replace. This comes with certain risks, as these facilities and the personnel who man them are in urban nodes such as Sanaa. Stockpiles of missiles represent another target, as requirements such as temperature-controlled storage limit an opponent’s capacity to distribute them. Though these storage sites are hardened and buried, they can be struck with some existing maritime strike capabilities such as the Tomahawk Block V. The boats which may be used to cue UAVs like the Samad could also be struck.

In Sum

The Houthis’ maritime strike capabilities are technically advanced but lack targeting sophistication. They therefore represent a manageable threat that can be countered with air defence assets in the region, providing that Iran does not improve target cuing for the Houthis. However, the Houthis are a persistent and determined opponent, and it is unlikely that they will halt their strikes simply because they are ineffective. This makes direct coercion to stop them more likely. The most effective course of action would involve strikes against limited but valuable target sets within the Houthi organisation. Doing so would impact the group’s ability to continue its missile strikes while minimising the risk of a wider regional conflict, thereby enabling the US and other navies to free up capacity for other strategic concerns.

Sam Cranny-Evans was a Research Analyst at RUSI in C4ISR between October 2021 and December 2022. During his time at RUSI he focused on multi-domain integration, electronic warfare, and the war in Ukraine. He co-led the establishment of the Red Team project, which provides analysis of the Russian and Chinese militaries. He has also spent time researching lethal autonomous weapons and their proliferation risk. He now works at Helsing, a defence AI company providing thought leadership and in government affairs.

Sidharth Kaushal is the Research Fellow of Sea Power at RUSI. His research covers the impact of technology on maritime doctrine in the 21st century and the role of sea power in a state’s grand strategy.