A New Threat in the Red Sea: Houthi UUVs

In this 2022 file image, Iran's Islamic Revolutionary Guard Corps displays a new model of torpedo-shaped drone submersible. Iran provides advanced weaponry to the Houthi movement (IRGC file image)

Published May 21, 2024 7:50 PM by CIMSEC


[By Commander Amila Prasanga, Sri Lankan Navy]

The Red Sea, a narrow waterway snaking between Africa and the Arabian Peninsula, serves as a vital route for global trade. Significant energy resources transit the Red Sea, including an estimated 12 percent of total seaborne-traded oil in the first half of 2023, and liquefied natural gas (LNG) shipments that account for about 8 percent of worldwide LNG trade. However, this crucial passage now faces a new and unexpected threat – Unmanned Undersea Vehicles (UUVs) deployed by the Houthi rebels in Yemen.

The Houthis’ use of UUVs marks a significant escalation in the ongoing Red Sea crisis. These submersible drones, while not as sophisticated as military submarines, pose a significant challenge to naval operations designed primarily to counter surface and aerial threats. The emergence of the Houthi UUVs threat necessitates a comprehensive reassessment of the naval defense strategies and tactics being employed in the Red Sea.

How can coalition forces adapt Red Sea operations to enhance undersea defense against unconventional threats such as Houthi UUVs? What steps are required to restore stability in the Red Sea region, emphasizing a decisive response to the Houthi UUVs threat? Furthermore, how must global navies adapt their warfighting techniques to effectively counter the distinct challenges posed by these emerging undersea threats?

By effectively addressing these critical questions, the international community can ensure the safety of vital sea lanes in the Red Sea and establish a framework for countering emerging undersea threats in the future.

Houthi UUV Capabilities and the Evolving Threat

The Houthi rebels in Yemen have injected a new and unsettling element into the Red Sea’s already tense security landscape. In March three undersea telecommunication cables were cut in the Red Sea, which the Houthis have denied doing, but nonetheless suggests a contested undersea domain. While details about Houthi UUVs remain murky, open-source intelligence suggests they are likely commercially-adapted or relatively unsophisticated submersible drones. Despite their presumed lack of sophistication compared to military submarines, these low-cost UUVs pose a significant threat due to several key factors.

The operational range and payload capacity of Houthi UUVs are currently unknown. However, even a modest range, measured in tens of miles, could enable them to target commercial shipping within the Red Sea. Their potential payload could include mines, torpedoes, or explosives packed into the hull, possibly enough to inflict significant damage on unsuspecting commercial vessels.

Houthi UUVs likely lack sophisticated guidance and targeting systems compared to military-grade undersea drones. They may rely on basic GPS or pre-programmed routes, as well as wire guidance. However, this simplicity can also make them difficult to detect and eliminate before they reach their targets.

Traditional naval defenses designed to counter surface and aerial threats are largely ineffective against undersea drones. Sonar technology and undersea surveillance systems are crucial for detecting and tracking UUVs. The preferable escort and maneuver patterns of warships searching for undersea threats may be at odds with the operational patterns that optimize air defense coverage, potentially creating difficult tradeoffs and tensions. This can create a significant challenge for the international coalition forces operating in the Red Sea.

The impact of Houthi UUVs extends far beyond potential damage to individual ships. The very presence of undersea threats is disruptive, given how the stealth of undersea platforms can magnify the effects of their operations and substantially shape the behaviors of those under threat. According to a recent report by the Global Trade Research Institute, even minor disruptions to Red Sea shipping could have a cascading effect on economies in Asia, Africa, and Europe. The specter of undersea threats can stimulate outsized uncertainty and risk, potentially driving up insurance costs and impacting global supply chains further.

Responses and Challenges in a Multi-Domain Environment

Faced with Houthi UUVs lurking beneath the waves, the international coalition in the Red Sea is grappling with a new and demanding challenge. However, the coalition is not without options. There are various strategies and capabilities that can be employed by coalition forces.

Mine Countermeasures warships (MCMs) are crucial for clearing mines potentially deployed by the Houthis, which can be deployed by the UUVs in sea lanes and also deployed near the UUV launch sites. The sonar and mine disposal capabilities of MCM ships can play a vital role in safeguarding sea lanes and improving undersea domain awareness.

Anti-Submarine Warfare (ASW) capabilities can be adapted to the UUV fight, including sonobuoys, towed array sonars, dipping sonars, and deployable hydrophone arrays. These tools can help create a more comprehensive undersea surveillance network in the Red Sea and gather critical intelligence on the telltale signatures of UUVs. An undersea surveillance network can be useful for cueing UUV hunters toward detections, rather than relying hunters to find UUVs using only their organic sensors.

The information-intensive nature of surveilling the complex undersea domain demands thoughtful approaches to intelligence coordination. Information sharing and collaboration among coalition members is critical for locating Houthi UUVs. Real-time data exchange can help predict potential attacks and enable a more coordinated response. Faster reaction times and improved targeting capabilities could potentially be used to intercept Houthi support vessels or launch platforms before they deploy UUVs. Ultimately coalition forces can aspire to strike Houthi UUVs before they are ever deployed by degrading their enabling infrastructure.

Despite the possibility of adaptation, current undersea surveillance capabilities may not be optimal for detecting low-signature Houthi UUVs, particularly in the acoustic environment of the Red Sea. The maritime shipping that continues to transit may transmit significant sound into the undersea environment that complicates UUV hunting, especially as a UUV nears a target merchant vessel. Advanced undersea drones and sensor networks specifically designed for UUV detection are urgently needed. Employing new tactics for UUV detection, engagement, and neutralization will require tailored training and exercises that realistically simulate hostile UUV encounters.


The Red Sea crisis serves as a pivotal moment in the evolution of maritime security. The lessons learned here – the importance of adapting naval power, the dangers of escalation, and the necessity of international cooperation – will reverberate far beyond the shores of this strategically vital waterway. By embracing innovation, fostering collaboration, and developing effective strategies for the undersea battlefield, the international community can ensure the safety and security of global trade routes and navigate the challenges of the 21st-century maritime security landscape.

Forces must consider what adaptations can meet the emerging UUV threat. Investing in cutting-edge drone detection and undersea surveillance systems is crucial for creating a comprehensive UUV defense network. Research and development efforts should focus on advanced sonar technologies and autonomous undersea vehicles (AUVs) specifically designed for UUVs countermeasures. Improved intelligence gathering and information sharing among coalition partners is essential for tracking UUVs and anticipating potential attacks. This includes intelligence cooperation with regional partners and leveraging advanced surveillance technologies.

The Red Sea crisis underscores the importance of international cooperation in addressing emerging maritime threats. Sharing best practices, conducting joint training exercises, and fostering closer collaboration on technology development are all crucial steps towards a more robust response to UUVs. The Houthi UUV threat offers a stark reminder of the need for continuous adaptation and innovation in the realm of naval warfare. Long-theorized unmanned undersea threats have now arrived.

Commander Amila Prasanga, Sri Lankan Navy, is Military Research Officer at the Institute of National Security Studies, the premier Sri Lankan think tank on national security, established and functioning under the Sri Lankan Ministry of Defence. The opinions expressed are his own and are not necessarily reflective of the official views of the institute or the Ministry of Defence.

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The opinions expressed herein are the author's and not necessarily those of The Maritime Executive.