Can RF monitoring protect commercial shipping against counter-targeting threats?

Recent threats to commercial shipping in the Red Sea demonstrate the need for enhanced counter-targeting procedures for commercial vessels. With installed spectrum monitoring systems, shipping companies can significantly increase the safety and security of commercial vessels sailing in high-risk areas by making themselves a more challenging target to detect. Reducing insurance costs through enhanced awareness of jamming or executing an emission control strategy may also be possible. 

Commercial ships: easy targets during conflicts

Large commercial ships have always been easy targets during global conflicts, particularly in the Middle East. From Iranian and Iraqi attacks on each other's oil tankers during the Iran-Iraq war to the Iranian Islamic Revolutionary Guard Corps attacks on commercial ships in the Strait of Hormuz and the Gulf of Oman in 2019 and 2020, commercial shipping during military conflicts has proved vulnerable. 

Recent threats to commercial shipping in the Middle East led to the US and its allies implementing various measures to increase the safety and security of maritime shipping in international waters. The French-led European Maritime Awareness in the Strait of Hormuz (EMASoH) mission, which began in 2020, was one of these measures.

US Navy vessels and US Air Force combat aircraft deployed to the Middle East protected commercial shipping in the Strait of Hormuz and the Gulf of Oman as well as in the north Arabian Sea and Gulf of Aden until November 2023, when Houthi rebels in Yemen began attacking commercial vessels. They are now threatening the safety and security of maritime shipping, this time in the Red Sea, Bab El-Mandeb Strait, and Gulf of Aden.

Despite deploying allied forces deploying several destroyers, frigates, submarines, and an aircraft carrier, there have been several successful attacks from land-attack cruise missiles, anti-ship missiles, ballistic missiles, and suicide (or kamikaze) drones targeting commercial ships since November 19, 2023.

The threat of attack and hijacking has led several shipping companies to temporarily avoid the Red Sea and Gulf of Aden due to increased insurance costs—which subsequently increased the cost of some goods, including petrochemicals.

How have the Houthis attacked commercial ships?

  • 11 attempted hijacks using equipment such as a Mil Mi-171Sh utility helicopter and speedboats
  • 22 attacks using anti-ship missiles, ballistic missiles, land-attack cruise missiles, and kamikaze drones and boats
  • 9 suicide drone attacks used drones such as the Sammad-1 and Shahed-136
  • 5 used anti-ship missiles, land-attack cruise missiles, and anti-ship ballistic missiles
  • 1 was a combined drone strike and hijacking attempt
  • 1 attack used an unmanned surface vessel 
  • 7 used a combination of suicide drones and anti-ship missiles

How could the Houthis be using RF tech against commercial ships?

While the exact targeting systems and procedures have not been revealed in open reporting, large commercial vessels can be targeted visually or by tracking AIS (161.975 or 162.025MHz) and other associated maritime RF signals, including VHF bridge to bridge communications and navigation radars.

Having rudimentary commercial RF spectrum analyzers or perhaps basic military-grade EW systems is enough to provide a line of bearing or a geolocation of the vessel of interest. As Houthis are targeting American and Israeli-flagged shipping, they are likely gathering information from an AIS database listing flag status.

Tracking a target vessel's AIS (via an open-source AIS website) and identifying a radar signal could be enough data to launch a strike—or dispatch small vessels for visual confirmation.

Ship Self-Defense Systems (SSDS)

Many military vessels are equipped with an SSDS. For example, many of the US Navy cruisers and destroyers, including the Arleigh-Burke class variants, are fitted with AN/SLQ-32 electronic warfare suites, which play a critical role in the operation of their SSDS.

The system acts as a threat warning system by receiving low-frequency, high-band radar signals commonly emitted by anti-ship missile terminal guidance radars and long-range surveillance radars. It can also detect high-frequency targeting and fire-control radars, providing early warning against an imminent anti-ship missile attack. The system can actively jam radars and anti-ship missile terminal guidance radars. In addition to radar jamming, these systems are interfaced with the Mk 36 Decoy Launching Systems, which can launch chaff and infrared decoys to evade radar-guided anti-ship weapons.

However, commercial ships are unlikely to be fitted with SSDS to protect themselves from anti-ship weapons. And only a small number use private military companies to protect their vessels from the threat of piracy. Therefore, allied forces have launched several maritime security operations, such as Operations Atlanta and Prosperity Guardian. Despite these actions, the commercial ships have continued to be targeted by Houthi rebels.

Commercial shipping and emission control (EMCON)

While naval vessels practice and execute emissions control (EMCON) and, at times, tactical deception, commercial vessels normally cannot do so due to insurance regulations and International Regulations for Preventing Collisions at Sea (COLREGS). However, commercial ships could theoretically carry out several actions to make their electronic footprint smaller, making the vessels harder to target with weapons. 

Using basic EMCON principles, they could:

  1. Lower transmission power on radars and radios
  2. Use prowords on an open communication net
  3. Chane callsigns every day (prior coordination with on-scene military command required)
  4. Broadcast AIS at longer intervals
  5. Use satellite communication more than terrestrial as satellite communications are harder to detect by terrestrial RF sensors due to their narrow beams pointed to space

While many mariners are not trained in these tactics, naval forces have formed convoys to protect commercial shipping. They could deploy experts (known in the US Navy as Strategic Sealift Tactical Advisors) onboard to educate and manage these types of procedures, as they did during the Battle of the Atlantic (WWII) or Operation Praying Mantis (1987–1988 in the Persian Gulf). Another option would be to include RF experts as part of onboard security teams hired by commercial shipping companies.

Commercial shipping and signal interference reporting

Interference at sea can be considered an act of aggression when it intentionally disrupts or hinders the legitimate activities of vessels, potentially leading to harm or conflicts. Although the US Navy must adhere to the Joint Spectrum Interference Reporting (JSIR) procedures for reporting interference, commercial ships are not required to report such interference formally.

However, there are pathways for commercial vessels to report radio interference or jamming to security or military forces. For example, NATO has an online form to report electronic interference within the Mediterranean Sea. This format could also be used within the Red Sea area as the United Kingdom Maritime Trade Operations (UKMTO) and Maritime Security Centre-Horn of Africa (MSCHOA) do not have standardized electronic interference reporting forms.

NATO Electronic Interference Report Format

Please report the following:

1.      DTG (Date Time Group)/ Unit LAT/LONG position at reporting time

2.      Track while observing interferences/ From LAT/LONG to LAT/LONG

3.      Duration while observing interferences - start and end time

4.      Interference type (systems affected and how?)

5.      Assessed direction or coverage area of interference

6.      Navigation: secondary modes of navigation usage and accuracy vs GPS systems

7.      Communications systems affected

8.      Overall assessment of observations - provide free text comments on the event and any additional information that is considered interesting


Commercial vessels and spectrum monitoring systems  

With no way to monitor the radio spectrum, mariners only know about radio interference and jamming when they need to use a radio system, and all they hear is static.

However, installed spectrum monitoring systems detect interference immediately, and they operate 24/7, which could help indicate trends and provide valuable data to allied military forces. While this threat has not yet been seen in the Red Sea, GPS and other interference has historically affected shipping in the Black Sea and Eastern Mediterranean.

The maritime industry is increasingly acknowledging the advantages of spectrum monitoring. Recently, the Bureau Veritas revised its Rules for Classification of Ships (NR467 F R16) to include a recommendation for spectrum monitoring systems spanning the frequency range of 9kHz to 18GHz on commercial vessels. These systems are intended to identify signal jamming, thereby aiding mariners in establishing a basic communications contingency plan, commonly referred to in military circles as "PACE."

What does the recommendation say?

Note 1: It is recommended to deploy means of radio spectrum analysis for interference detection, e.g. sensitive omni-direction receiver antenna with a control and processing unit interfacing the ship-shore communication system. The antenna for spectrum analysis should have a frequency range adapted to the ship's radio communication frequency range, e.g., 9kHz to 18GHz, and mounted clear from the ship's transmitting antennas, if the ship's dimensions permit. Early detection of jamming may be used to alert the operators and to automatically redistribute the traffic to the intact communication channels. The timestamped jamming data may be further submitted to the local spectrum regulation authorities for mitigation.


An installed spectrum monitoring sensor could feed into an integrated bridge system and send alerts to the ship's master and insurance company of a possible jamming event, meaning the ship's master or crew would not require RF expertise to operate the system.

Special considerations for autonomous shipping spectrum monitoring

While not presently operating in the Red Sea, unmanned surface vehicles (USVs) have an even greater dependency on the radio spectrum as they could operate without a single human onboard. An installed spectrum monitoring system can assist in automated communication reporting and fallback plans (PACE).


While it is not viable for commercial ships to employ military-grade SSDS, installing RF technology can enhance their safety and security. A sustained military campaign in the Red Sea is not a likely option—neither is rerouting all commercial vessels around the Cape of Good Hope. However, installing RF-Monitoring systems for counter-targeting and EMCON could be an effective measure to add another layer of protection for commercial ships against future attacks.

Babak Taghvaee

Babak Taghvaee is a defense and security journalist, researcher, historian, and book author based in Europe. With over 16 years of experience, he specializes in defense and security topics for various prestigious international publications. As an OSINT (Open Source Intelligence) expert, he has written hundreds of evidence-based reports and articles for news media such as Radio Free Europe, Israel Hayom, and the BBC.

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