By Logan Williams, Warrior Editorial Fellow
The Houthis are a Yemeni, Iran-backed, Shia Islamist insurgency, that has been terrorizing innocent sailors in the Gulf of Aden, the Strait of Bab-el-Mandeb, and the Red Sea for several months. The Houthi terrorists have insisted that these attacks upon global shipping are retribution for the West’s support for the Israeli people, who were themselves brutally attacked by terrorists, on October 7th, 2023.
The United States’ Navy acted swiftly in defense of unrestricted access to the Seas, an indispensable principle enshrined in over a thousand years of international cooperation – long predating Hugo Grotius’ seminal treatise on the subject, The Freedom of the Seas – and a principle without which the present liberal world order would be in dire jeopardy. These principles can be found within the UN Convention on the Law of the Seas (UNCLOS), to which approximately 164 nations are signatories, including Yemen — although, of course, terrorist groups have no respect for international law.
Within two weeks of Hamas’ monstrous terrorist assault upon Israeli civilians, the United States’ had one amphibious assault ship in the Red Sea, with two more on the way. The United States’ closest longtime partner – the United Kingdom, and France also sent vessels to join the United States’ fleet. On December 18, the United States announced the launch of Operation Prosperity Guardian (OPG), which added the support of eight additional states to the initial efforts of the United States, the United Kingdom, and France. Afterward, it was reported that ten more countries had chosen to get involved with OPG, but wished their involvement to remain anonymous; these countries are likely states in the Persian Gulf, who fear that their involvement will incite repercussions amongst radical elements at home.
Houthi Terrorists
The Houthi terrorists haven’t just effectively closed one of the most crucial sea shipping routes, responsible for the shipping of most of the fossil fuels produced in the Arab region, but these militants have also sought to maximize civilian casualties in the process.
The Houthis have access to ballistic missiles, sourced from Iran, and they certainly have not shied away from using them to strike civilian ships, but in recent years they have shifted towards favoring drone attacks, using Iranian one-way drones – drones rigged with explosives, designed to explode on contact with a target – in swarms, which can even overwhelm some air defense systems. Drones are cheaper to produce (costing just a few thousand dollars), and thus, are far easier to come by than ballistic missiles, making them the perfect tool for a terrorist seeking to sustain violence over a long period of time.
U.S. Navy vessels have been forced into a position in which the crew has to effectively and efficiently, track and destroy tens of these cheaply manufactured, flying IEDs, in one altercation. This is a mission for which the United States’ destroyers were not designed.
Warrior Discussion with Army Acquisition Executive
The United States Navy’s primary assets in the region, tasked with the defense of civilian vessels, are Arleigh Burke-class guided-missile destroyers, such as the USS Mason and the USS Carney. These destroyers are equipped with the Aegis Combat System, which is a centralized weapons control platform which combines the management of every weapon on a warship into one system. The Aegis was designed in the 1980s, to protect against the potentiality of a missile saturation attack (i.e., a swarm of missiles) by the Soviet Union, with missiles such as the KH-22 “Kitchen,” the Kh-26 “Kingfish,” or the KH–28. As such, the Aegis Combat System is said to be able to identify and track approximately 100 distinct targets, at once — although this statistic may be misleading.
While the Aegis can identify and track approximately 100 targets, at once, a vessel’s defensive systems can be overwhelmed by far fewer.
An Arleigh Burke-class guided-missile destroyer is equipped with a variety of weapons capable of managing a threat from drones.
The Arleigh Burke-class destroyers are equipped with the Mark 41 Vertical Launching System (Mk 41 VLS), paired with SM-2, SM-6, and RIM-162 Evolved SeaSparrow Missile (ESSM) ordinance.
As for guns, these destroyers possess a Mark-45 5-inch gun turret; two Mark-38 25 mm machine gun systems; and the infamous Phalanx CIWS — in addition to a number of Browning M2 machine guns mounted on various places of the ship.
It is believed that, until this point, the U.S. Navy destroyers in the Red Sea have been relying upon their various missiles to counter drones attacks. These missiles are the primary offensive and defensive weapon of the destroyer platform. Unfortunately, these missiles have a number of different limitations.
First, if a drone is too close to a vessel, the detonation of a missile launched to intercept and destroy the drone, could very well damage the ship that launched it — most of the missiles on the U.S. Navy’s destroyers shouldn’t be used to intercept a target within 500 meters of the vessel, itself.
Aegis Radar – Layered Ship Defenses
This poses a significant concern because drones, by their very nature, are difficult for radar to identify and track. When the Aegis Combat System was conceived in the 1980s, the types of missiles that it was designed to defend against had a radar cross section (i.e., radar signature) ranging from 10m2 to 0.1m2, and it was almost always closer to the former. Today’s Iranian-made drones can have a radar signature as small as 0.01m2, approximately that of a bird, or even smaller. Additionally, the Aegis has to differentiate this infinitesimally small radar signature from that of the radar clutter which is emitted by the ocean’s surface. If a drone swarm traveled as a pack, in tight formation, from the launch point to its target, it would have a much larger radar signature. However, if the operators were intelligent enough to fly variable trajectories, and to attack the ship from every direction, each individual drone would be very difficult – next to impossible – for the Aegis to identify. In 2012, a paper was written exploring the threat of drone swarming, and in the scenarios described in the paper, an individual drone was first identified by Aegis when it was approximately a mile from the vessel — which gives the crew a maximum of 30 seconds to successfully destroy the drone. Out of 8 drones, the author of this paper postulates that two are bound to get past a ship’s defenses.
Secondly, while the Aegis Combat System can track upwards of 100 individual targets, missiles require radar guidance, and these destroyers are not equipped with the necessary radar capability to successfully intercept 100 targets within a short timeframe.
< p>First, it is important to understand the two basic types of radar, in relation to threat detection and elimination. The first is a vessel’s main volume search radar, which is the AN/SPY-1 or the AN/SPY-6 on U.S. Navy destroyers; it may be easier to refer to this as a wide beam radar because it utilizes a broad transmit beam to search a large area and identify and display a variety of different targets on a radar screen. The second type of radar is called the fire-control radar, occasionally called a narrow beam radar, because its narrow beam is required for accurate guidance to a target. It is important to note well that the fire-control radar can only guide one missile at a time.
Second, it is crucial to understand that there are a variety of guidance technologies available for missiles, but the two most relevant for this discussion are semi-active radar homing (SARH) and passive radar homing. Passive radar homing is a system that requires guidance from a fire-control radar from the moment the missile is launched until the moment it strikes its target. Semi-active radar homing is a system which allows a missile to be launched on an intercept path with the trajectory of the target, as identified by the less accurate main search radar, and in the last seconds before impact, the missile can switch to guidance from fire-control radar to alter its course and intercept the target. The Aegis Combat System is capable of tracking each of the missiles launched from a U.S. Navy vessel, automatically performing the necessary switch into fire-control radar for each missile as it nears its target, thereby maximizing the amount of missiles that a fire-control radar can guide in any given period of time by time-sharing.
This means that the ability of a navy vessel to fend off a swarm attack is severely limited by the number of fire-control radars on the ship — Arleigh Burke-class guided-missile destroyers are equipped with three.
US Navy Destroyer vs Drone Swarm
As an illustration of this weakness, assume for a moment that a drone swarm of an unidentified number of Iranian-made UAVs is approaching a U.S. Navy destroyer, and as was suggested in the paper from 2012, the drones were detected approximately a mile from the ship. Assume, also, that the drone is a Wa’eed-2 type, an identical knock-off of the Iranian Shahed-136 type, which can travel at speeds of anywhere from 100 MPH-150MPH. The sailors aboard the U.S. Navy destroyer would have anywhere from 24-36 seconds to respond to the threat. Assuming that each SARH missile needs the last second of guidance with fire-control radar, a destroyer could likely fend off anywhere from 50-70 swarming drones. Of course, this is completely and unrealistically disregarding the safety of launching missiles that close to a vessel, and it is not including the time it takes for the crew to take action once the drones are spotted on radar, or a number of other confounding variables.
The three afore-mentioned missiles on board the Arleigh Burke-class guided-missile destroyer have different guidance systems; SM-2 is a SARH missile, SM-6 is an active radar homing missile – as in all the components for guidance are built into the missile and it doesn’t require ship-based radar, and the RIM-162 Evolved SeaSparrow Missile (ESSM) is a passive radar homing missile.
However, despite the obvious usefulness of active radar homing, the SM-6 is almost certainly overkill for anti-UAV missions, since it was designed with very high altitude and atmospheric anti-ballistic missile capabilities, in mind.
This makes the SM-2, the primary air-defense missile of the U.S. Navy, the ideal missile for fending off a drone swarm attack. Most experts believe that the U.S. Navy has been utilizing a combination of SM-2 and ESSM missiles against drones in the Red Sea. However, this exposes the third weakness of using missiles for anti-UAV tasks. The SM-6 costs over $4 million per missile; the SM-2 costs approximately $2.5 million per missile; and an ESSM costs more than $1 million per missile. The U.S. Navy intends to continue protecting the lives of innocent sailors traversing the Red Sea, because there is no price that can be placed upon the lives lost if a drone strikes a ship; however, there are legitimate concerns about the logic of expending millions of dollars to destroy a $10,000 drone.
This cost-disparity has led some talking-heads to question why ships are unable to use their guns to destroy drones. The short answer is because the guns on a U.S. Navy destroyer were not designed for that task.
The MK-45 5-inch ship gun was designed to offer fire support for marine expeditionary units and for limited anti-ship self defense capabilities. It is not a weapon designed for striking small targets. Many ship guns have a circular error probability (CEP) of upwards of 200 meters. This means that out of 100 shots taken, 50-percent will fall within a circle drawn around the target with a radius of 200 meters. As many shots will land over 200 meters away from a target as will land within that radius. The U.S. Navy has been excited by the concept of firing guided munitions from the MK-45, which can reduce the CEP to anywhere from 50 meters to 5 meters. For reference, the wingspan of Iran’s ubiquitous drones is approximately two or three meters. In other words, there is no projectile in existence which can hit a drone when fired out of a MK-45 ship gun, outside of sheer dumb luck or a miracle.
The MK-38 machine gun, which can fire upwards of 175 rounds a minute, may have some utility against low-flying drones. However, the MK-38 can only engage one drone at a time. More importantly, the MK-38 has restricted mobility, it cannot be elevated to an angle above 40-degrees, which severely limits its ability to engage higher flying drones or serve any other air defense function.
Destroyers’ last line of defense is the Phalanx CIWS system, which is designed to engage targets that have penetrated each of the other defenses, and which are less than a few miles from the ship. The CIWS system is incredibly effective against drone swarms. It is designed to blanket an area with 20mm bullets, fired at 4500 rounds per minute, but it can effectively only engage one target at a time.
A U.S. Navy destroyer’s Browning M2 machine guns, like all crew-served weapons (CSW), would likely be next to useless in combating a drone swarm. Unless the vessel was already at general quarters, the time that it would take for sailors to reach the machine guns, let alone load them, would certainly be all the time that the drones would need to strike and detonate.
Electronic Warfare & Lasers
There is another defense mechanism, however, which emerges from these vessels’ electronic warfare (EW) capabilities. An interesting news report published by the United States Naval Institute described how a U.S. Navy vessel was able to take down a Houthi drone with the Marine Corps’ new Marine Air Defense Integrated System (MADIS). MADIS is an EW system, mounted atop a vehicle, designed to provide a Marine expeditionary unit mobile EW and localized air-defense capabilities. The MADIS has the ability to detect drones with incredibly small radar signatures, it has the ability to disrupt those drones’ communications, and it has the ability to spoof the drones’ navigation, thereby allowing the MADIS operator to take control of an enemy drone and fly it to a desired location. Sy
stems such as the Tactical High-power Operational Responder (THOR), utilize microwave signals to cause drones to fall out of the sky. In fact, many U.S. Naval destroyers have been equipped with an EW device called the Optical Dazzling Interdictor Navy (ODIN). However, little is known about the operational capabilities of ODIN, and there is no way to ascertain whether it has the capability to disable or destroy the Iranian-made drones that seem to proliferate so rapidly.
In the short-term, it seems that the U.S. Navy has little choice but to continue launching million-dollar missiles at drone targets, lest it let terrorists establish control over one of the most important shipping routes in the world, and slaughter civilians in the process. In the long run, however, the U.S. Navy should take this conflict with the Houthis as an opportunity to learn important lessons about the future of asymmetric naval warfare, and begin to seriously invest in realistic ship-based EW capabilities that can protect against this emerging tactic of kamikaze, IED-drone swarms.
Williams is a Warrior Editorial Fellow and is a writer and researcher currently studying at the University of Connecticut. Williams’ work has been published in newspapers, magazines, and journals, such as:, Geopolitics Magazine, Modern Diplomacy, The Fletcher Forum of World Affairs, Democracy Paradox, Diario Las Américas, International Affairs Forum, Fair Observer, History Is Now Magazine, American Diplomacy, etc.
