Targeting Iranian Spy Ships
On March 17, 2025, Al-Hadath, a Saudi news outlet, reported that U.S. forces in the Middle East had targeted and sunk Iran’s newest signals intelligence (SIGINT) ship, the IRINS Zagros (H313), while the spy ship was on station in the Red Sea. Both U.S. and Iranian officials immediately denied the report, which was subsequently retracted by Al-Hadath.
The unconfirmed report comes on the heels of a post on Truth Social by President Donald Trump indicating the United States would hold Iran accountable for its support to the Houthi rebels.
Every shot fired by the Houthis will be looked upon, from this point forward, as being a shot fired from the weapons and leadership of IRAN, and IRAN will be held responsible, and suffer the consequences, and those consequences will be dire! Let nobody be fooled! The hundreds of attacks being made by Houthi, the sinister mobsters and thugs based in Yemen, who are hated by the Yemeni people, all emanate from, and are created by, IRAN. Any further attack or retaliation by the ‘Houthis’ will be met with great force, and there is no guarantee that that force will stop there. Iran has played ‘the innocent victim’ of rogue terrorists from which they’ve lost control, but they haven’t lost control. They’re dictating every move, giving them the weapons, supplying them with money and highly sophisticated Military equipment, and even, so-called, ‘Intelligence.’
U.S. National Security Advisor Mike Waltz elaborated on the President’s post, indicating the United States would consider expanding its offensive campaign against the Houthis by targeting Iranian assets assisting the rebels.
We will hold not only the Houthis accountable, but we’re going to hold Iran, their backers, accountable as well. If that means … targeting [Iranian] ships [providing intelligence] … Iranian trainers, IRGC and others, … other things that they have put in to help the Houthis attack the global economy, those targets will be on the table, too.
Assuming the Saudi report was true—that the United States did sink the Zagros—would the United States be legally justified in attacking, in self-defense, Iranian ships and Islamic Revolutionary Guard Corps (IRGC) personnel providing actionable intelligence, targeting data, and other direct military-related support to the Houthis? The short answer is yes.
Iranian Spy Ship Capabilities
For more than a decade, the IRGC Navy (Nedaja) has maintained a forward presence of commercial vessels in the Red Sea and the Gulf of Aden that serve as auxiliary intelligence ships. These vessels play an important role in collecting intelligence on international shipping and disseminating that information to the Houthi rebels in Yemen. Two of these vessels—M/V Saviz and M/V Behshad—have maintained a near-constant presence off the coast of Yemen since 2016 and have been linked to providing direct support to the Houthis. By fusing all-source intelligence with Automatic Identification System (AIS) information gathered from transiting commercial vessels, these ships are “able to maintain an accurate maritime area activity plot” that can be disseminated to the Houthis to facilitate targeting of international shipping off the Arabian Peninsula. Both vessels were sanctioned by the first Trump administration in 2018.
The M/V Saviz is State-owned by the Islamic Republic of Iran Shipping Lines (IRISL) and registered with the International Maritime Organization (IMO) as a cargo vessel. The Saviz arrived in the Red Sea in 2016 and loitered off the coast of Eritrea until 2021 when it was damaged by an explosion caused by a limpet mine planted on its hull (attributed to Israel).
Although Iran claimed the Saviz was deployed to the region to assist in its anti-piracy efforts in the Red Sea and the Bab al-Mandeb Strait, the IRGC was in fact using the vessel as a base to provide weapons, intelligence, and logistical support to the Houthis. The Saudi military reported that personnel on board the vessel wore military-style camouflage fatigues and that the ship’s three small speedboats ferried weapons and other military cargo to the Houthis in Yemen. The vessel was also equipped with intelligence domes and antennae that were unusual for a cargo ship, suggesting it was conducting electronic surveillance. The spy ship additionally features .50-caliber machine gun mounts. The Saviz reportedly provided command and control and targeting data for Houthi attacks on commercial shipping in the Red Sea and the Bab al-Mandeb Strait.
Saviz was replaced by the M/V Behshad after Iran towed the Saviz back to Bandar Abbas in April 2021. The Behshad is also registered with the IMO as a cargo vessel and is State-owned by the IRISL. Like its sister ship, Behshad is manned by personnel wearing military-style uniforms and has engaged in unusual activities off the coast of Yemen (e.g., remaining stationary off the coast of Eritrea, being guarded by Nedaja vessels, and periodically turning off its AIS transponder). The surveillance ship is equipped with three maritime radar arrays, giving it a 50-nautical mile detection range. It can also receive one-meter resolution imagery from Iranian and Russian satellites and routinely communicates directly with the Houthi fishing fleet intelligence collectors. Behshad can also use its small speedboats to collect intelligence or for scouting purposes.
In January 2024, Behshad was forced to leave its position in the Red Sea off the coast of Eritrea and relocate to the Gulf of Aden about 100 kilometers east of the port of Djibouti. Because the Houthis do not control the coastline along the Gulf of Aden, positioning the Behshad off Djibouti made it easier for the Houthis to locate and target ships transiting the Gulf. After the United States reportedly conducted a cyber-attack against Behshad to disrupt its targeting assistance to the Houthis, the spy ship returned to Bandar Abbas in April 2024.
Iran launched the IRINS Zagros (H313), Nadeja’s newest, domestically built SIGINT ship on January 15, 2025. The intelligence ship is equipped with electronic sensors that can be used to “collect, decrypt, and analyze radio-frequency signals from hostile … emitters.” The antennas for these sensors, as well as satellite communications systems, are housed in three large ball-shaped radomes on the top of the ship’s superstructure. The ship lacks armaments of any kind but is equipped with a radio direction-finding antenna mounted on the ship’s mast and a flight deck and hangar bay capable of accommodating an Agusta-Bell AB212 helicopter. An embarked helicopter could be used to provide logistical support and force protection or to increase the range of the ship’s intelligence collection capabilities. The Zagros can also reportedly conduct cyber operations. In short, the surveillance ship provides Iran with a new and improved capability to gather intelligence to support the Houthi’s anti-shipping campaign off the Arabian Peninsula.
Right of Self-Defense
Under customary international law, all States retain the inherent right of individual and collective self-defense reflected in Article 51 of the UN Charter (Department of Defense (DoD), Law of War Manual, § 1.11.5). This includes the right to exercise self-defense in response to an imminent attack (Commander’s Handbook on the Law of Naval Operations (NWP 1-14M), ¶ 4.4.1). Any measures taken in self-defense, however, must be necessary and proportionate to the threat being addressed (DoD, Law of War Manual, § 1.11.5; NWP 1-14M, ¶ 4.4.1).
The United States interprets the term “armed attack” in Article 51 consistent with the customary practice that allows a State effectively to protect itself from every illegal use of force aimed at it (DoD, Law of War Manual, § 1.11.5.2). Therefore, under the U.S. Standing Rules of Engagement (SROE), U.S. commanders have the inherent right and obligation to exercise unit self-defense in response to a hostile act or demonstrated hostile intent, which includes the defense of other U.S. military forces in the vicinity (Operational Law Handbook (OPLAW HB), p. 107). When authorized by the President or Secretary of Defense, U.S. commanders may also engage in collective self-defense of designated non-U.S. military forces and/or designated foreign nationals and their property from a hostile act or demonstrated hostile intent (OPLAW HB, p. 107).
The SROE define a hostile act as an attack or other use of force against the United States, U.S. forces, or other designated persons or property (OPLAW HB, p. 108). An example would be launching a missile or one-way attack drone at a U.S. warship. Hostile intent is defined as the threat of imminent use of force against the United States, U.S. forces, or other designated persons or property (OPLAW HB, p. 108). In determining whether the use of force is imminent, which does not necessarily mean immediate or instantaneous, U.S. forces at any level will assess all the facts and circumstances known at the time (OPLAW HB, p. 108). When responding to a hostile act or demonstration of hostile intent, U.S. forces may use all necessary means available and all appropriate action to respond decisively to the hostile act or hostile intent (OPLAW HB, p. 108).
Since October 2023, Houthi forces have launched over 140 attacks on merchant vessels and more than 170 attacks on U.S. warships in the Red Sea and Gulf of Aden, using hundreds of ballistic and cruise missiles, one-way attack drones, and explosive-ladened unmanned surface and underwater vehicles. In response, U.S. and coalition forces participating in Operation Prosperity Guardian have shot down countless Houthi missiles and drones in international airspace in self-defense. Based on the totality of the circumstances, each commander correctly assessed that the incoming missiles and drones posed an imminent threat to their units, as well as other U.S. and coalition forces and commercial shipping in the vicinity, and lawfully exercised the right of individual (unit) and collective self-defense.
Although the flag State is normally responsible for protecting its vessels operating beyond the territorial sea of another State, U.S. forces were apparently authorized by the Secretary of Defense to exercise collective self-defense to protect foreign-flagged vessels from unlawful acts of violence when requested by the flag State or the vessels’ master (UN Convention on the Law of the Sea, art. 92). Collective self-defense is also exercisable in cases where the necessity to act immediately to save human life does not allow time to obtain flag State or master consent (NWP 1-14M, § 3.10.2).
Similarly, land-based strikes conducted in self-defense on military objectives in Yemen by U.S. and coalition forces participating in Operation Poseidon Archer are also legally justified under international law. Generally, a State may only use force in the territory of another State with the consent or at the invitation of that State (DoD, Law of War Manual, § 1.11.4.3). Nonetheless, every State has an “obligation not to allow knowingly its territory to be used for acts contrary to the rights of other States” (Corfu Channel Case, p. 22; U.S. v. Arizona, p. 484). If a State (like Yemen) is unwilling or unable to stop an organized armed group (like the Houthis) from using its territory as a base of operations from which to launch attacks against another State, an aggrieved State (like the United States) may exercise its right of self-help and target the armed group within the territory of the unwilling State.
The Houthis control broad swathes of territory bordering the Red Sea that are not accessible to Yemeni security forces. The legitimate government of Yemen has therefore been unable or unwilling to prevent the Houthis from using this territory to launch attacks against international shipping and foreign warships in the Red Sea and the Gulf of Aden. Under these circumstances, U.S. and coalition forces may legally use force in self-defense against Houthi launch sites and other military facilities in Yemen (e.g., underground weapons storage facilities; command and control centers; drone storage, manufacturing, and operation sites; missile systems and storage facilities; radar sites; air defense systems; munitions depots; helicopters and other military equipment; fuel depots and power stations) to prevent future attacks from rebel-controlled territory. Although the right of self-help is not universally accepted by the international legal community, a growing number of States support such self-help measures.
Targeting Iranian Assets
In addition to providing targeting data and intelligence to the Houthis, there is abundant evidence that the IRGC has provided the Houthis with a “growing arsenal of sophisticated weapons and training that they have used to attack commercial shipping in the Red Sea” since at least 2014. Low-cost, advanced attack drones with extended range and explosive payloads allow the Houthis to “threaten territorial sovereignty, regional stability, and the global economy.” Iran has also provided the rebels with an arsenal of “short- and medium-range ballistic missiles and cruise missiles, including anti-ship variants,” which enhance their ability to attack maritime targets off the Arabian Peninsula. All these transfers are flagrant violations of UN Security Council Resolution 2216, which imposed an arms embargo on the Houthis.
There is also growing evidence that Iranian officials are directly involved in Houthi activities and decision-making. A report by the National Council of Resistance of Iran, for example, indicates that Iranian Supreme Leader Ayatollah Ali Khamenei personally supervises all Houthi political and military activities, emphasizing the importance of Houthi attacks on international shipping. Additionally, one of the most senior IRGC commanders—Brigadier General Abdolreza Shahlai—purportedly directs all Houthi operations and attacks.
By analogy, during an international armed conflict, neutral merchant vessels that take a direct part in the hostilities on the side of the enemy acquire enemy character. A belligerent may accordingly treat them as an enemy warship and attack, destroy, or capture them anywhere beyond neutral territory (DoD, Law of War Manual, § 15.14.2.1; NWP 1-14M, § 7.5.1, § 8.6.1). A merchant vessel that makes an effective contribution to military action or the exercise of any other belligerent rights on behalf of the enemy becomes a military objective and liable to attack by a belligerent. Activities considered to make an effective contribution to military action or the exercise of a belligerent right on behalf of the enemy include, inter alia: 1) engaging in belligerent acts, including gathering intelligence or providing targeting data; 2) engaging in activities otherwise performed by naval auxiliaries, such as carrying military material or war-sustaining material (e.g., fuel and food for use by the enemy’s armed forces); and 3) being incorporated into or assisting the enemy’s intelligence or military data-gathering systems, including reconnaissance and C-3 (command, control, and communications) missions in support of enemy forces (Newport Manual on the Law of Naval Operations, § 8.6.3).
The same analysis would apply to the use of force in self-defense in times of peace. If Houthi missile and drone attacks on commercial shipping and foreign warships trigger the right of self-defense under international law, the provision of actionable intelligence and real-time targeting data by Iranian spy ships (registered with IMO as merchant ships) to facilitate those attacks also triggers the right of individual (unit) and collective self-defense against those vessels.
Conclusion
The Trump Administration has put Iran on notice that the United States will hold it accountable if it continues to support the Houthis. Providing real-time targeting data is no different than launching a ballistic missile or one-way attack drone. Iran will bear responsibility and suffer the consequences of its actions. The days of playing “the innocent victim of rogue terrorists” are over for Iran. Tehran has not lost control of the Houthis but rather is dictating every Houthi move. The IRGC is providing the rebels with weapons and other sophisticated military equipment, as well as actionable intelligence and real-time targeting data, so they can continue their assault on global trade. It should therefore come as no surprise to Iran if (in the near term) U.S. forces attack Iranian spy ships that gather and provide intelligence and real-time targeting data to the Houthis to facilitate their attacks on commercial shipping and foreign warships in the Red Sea and Gulf of Aden.
The views expressed in this article are those of the author and do not necessarily represent the views of the Department of Defense, the Department of the Navy, or the U.S. Naval War College.
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Raul (Pete) Pedrozo is the Howard S. Levie Professor on the Law of Armed Conflict at the Stockton Center for International Law, U.S. Naval War College, Newport, Rhode Island.
The views expressed are those of the author, and do not necessarily reflect the official position of the United States Military Academy, Department of the Army, or Department of Defense.
Articles of War is a forum for professionals to share opinions and cultivate ideas. Articles of War does not screen articles to fit a particular editorial agenda, nor endorse or advocate material that is published. Authorship does not indicate affiliation with Articles of War, the Lieber Institute, or the United States Military Academy West Point.
Photo credit: Fars Media Corporation, Hossein Velayati
