Iranian involvement in missile attacks on the USS Mason
Iran almost certainly played a role in the missile attacks against the USS Mason near the Bab al Mandab Strait on October 9 and October 12. Senior U.S. administration officials asserted with “great confidence” that al Houthi forces were “unquestionably involved” in the missile strikes. U.S. officials have not identified the operatives directly responsible for targeting the U.S. warship or the origin of the weapons used in the attack. Iran likely supplied the missiles and, at the very least, Iranian Islamic Revolutionary Guards Corps Quds Force (IRGC-QF) or Lebanese Hezbollah operatives provided technical expertise and modifications in support of those who launched the attack. Iran or its proxy, Lebanese Hezbollah, may have also played a direct role in planning and conducting the attack.
The al Houthi-Saleh faction does not benefit from the deliberate targeting of U.S. Navy vessels, which would draw the U.S. further into the Yemeni civil war on the side of the Saudi-led coalition. Al Houthi-Saleh leaders have denied repeatedly responsibility for the USS Mason attacks in contrast with their rapid claim to have attacked the Emirati HSV-2 Swift on October 1. They have also taken steps to de-escalate tensions with the United States. Al Houthi-Saleh leaders released two Americans detained in Yemen to Oman on October 15. They also agreed to a 72-hour ceasefire and to return to political negotiations to resolve the civil war, steps U.S. Secretary of State John Kerry has advocated.
Attacking U.S. Navy vessels does serve Iran’s broader strategic objectives of countering U.S. and Saudi presence in the region, however. Iran has a clear interest in creating and signaling its deterrent capabilities off the Yemeni coast as part of its larger effort to increase the risk to U.S. maritime operations in the region. Iran has recently escalated the harassment of U.S. Navy vessels and senior regime officials have publicly called upon the U.S. to “end its presence” in the Persian Gulf. 
The following questions explore the nature and intent of Iran’s support for the al Houthi-Saleh faction, as well as the regional context, defined by conflict with Saudi Arabia and the West, in which Iran operates.
Yes. IRGC-QF or Lebanese Hezbollah operatives almost certainly played a role in supporting and possibly conducting the missile attacks.
- Iran likely supplied the missiles fired at the USS Mason, although the exact missile type used against the USS Mason has not yet been confirmed. Senate Armed Services Committee Chairman John McCain stated on October 13 that Iran likely provided the missiles used in the attacks. Iran probably would have supplied C-802 Noor anti-ship cruise missiles, an Iranian variant of the Chinese Silkworm that Iran has provided Hezbollah in the past. Iran has provided the al Houthi-Saleh faction with missiles before, including missiles used in cross-border attacks on Saudi Arabia, according to Secretary of State John Kerry and State Department Spokesman John Kirby. Alternately, the attackers may have repurposed C-801 anti-ship cruise missiles from Yemen’s pre-war arsenal.
- Iran or its proxy Lebanese Hezbollah almost certainly provided training, technical, or targeting support to the forces that conducted the attacks, even if the missiles originated from Yemen’s pre-war arsenal. The ground-based radar systems reportedly used in the attacks require sophisticated technical expertise, which al Houthi-Saleh forces would unlikely possess on their own. Even if the al Houthi-Saleh forces were able to fire the older C-801s that were originally installed on Yemeni missile boats, the use of ground-based radar systems in the attacks against the USS Mason would indicate technical support from Iran or Hezbollah.
- Iranian or Hezbollah operatives operating in Yemen may have been directly involved in conducting the attacks. The effects that attacks against U.S. Navy vessels generate advance Iranian interests in the regions. The al Houthi movement is not an Iranian proxy and does not respond to Iranian directives, making it less likely that Tehran ordered an attack and the al Houthi-Saleh faction carried it out. Al Houthi-Saleh leaders’ reactions to the attack—the denial of responsibility and steps to de-escalate tensions—could be taken as indicators that the leadership did not support attacks against the U.S. There is an additional possibility that a hardline al Houthi faction conducted the attacks with top-level technical support independent from al Houthi-Saleh or Iranian orders. In this case, the attacks may have been intended as a bid for additional Iranian support.
What is the nature of Iranian support for the al Houthi-Saleh faction?
Iran’s footprint in Yemen is relatively small. Tehran supports the al Houthi-Saleh faction with weapons, training, and limited funding. Iran dedicates far fewer resources to the Yemen conflict than its rival, Saudi Arabia, but Iran’s investment is sufficient to advance its strategic objectives in the country.
- Lebanese Hezbollah operatives have trained with the al Houthis in both Iran and Yemen. Hezbollah fighters have bragged about fighting in Yemen, though their claims are not independently verified. The IRGC-QF deputy commander publicly confirmed that Iranian forces were training the “defenders of Yemen,” likely a direct reference to the al Houthis, in a May 2015 speech.
- Iran provides medical assistance and limited financial support to the al Houthi-Saleh faction. The extent of Iran’s financial support is difficult to discern from open sources.
- Iran provides light and medium weaponry to the al Houthi-Saleh faction. Interdicted weapons shipments have included rocket-propelled grenades, light machine guns, and AK-47 assault rifles. This type of support is too limited to affect the al Houthi-Saleh faction’s capabilities in any significant manner, but sufficient enough for Tehran to claim its support for the faction.
- The absence of an open supply route limits Iran’s capacity to move materiel into Yemen. Iran cannot fly supplies into Yemen with commercial aircraft, as it does in Syria, due to the presence of Saudi and other Arab air assets. Weapons transfers by sea have proved to be vulnerable to interdiction even before the Saudi-led coalition’s loose blockade of Yemeni ports. Iran likely moves small shipments across the Yemeni desert via Oman.
- Iran supports the al Houthi-Saleh faction’s missile program, but the extent of support is unclear. The al Houthi-Saleh faction’s use of reengineered S-75 surface-to-air missiles as unguided surface-to-surface rockets is one indicator of Iranian-Hezbollah expertise. Expanded Iranian assistance, particularly in missile development, could increase the threat that the al Houthi-Saleh faction poses to southern Saudi Arabia and the Red Sea.
What is the intent of Iranian support for the al Houthis?
Iranian support for the al Houthi-Saleh faction is intended to pressure Saudi Arabia, as well as counter the U.S. and its regional allies. It also enables Iran to take actions that affect critical Red Sea shipping routes.
- Iran perceives itself as a regional hegemon and leader of the Muslim world. It actively supports Muslim groups and states to expand its influence. The Iranian regime recognizes the al Houthis as part of its network of proxies, partners, and allies throughout the region, including Iraqi Shi’a militias and the Assad regime. Iran relies upon this network to “resist” the U.S. and its regional allies, such as Saudi Arabia.
- Iran calibrates and times its support for the al Houthi-Saleh faction in order to enable a partner that can threaten and pressure Saudi Arabia. Its limited assistance to the al Houthi-Saleh faction probably reflects the regime’s assessment that it does not need to invest heavily to embroil Saudi Arabia in the Yemeni conflict. Iranian officials recognize the conflict in Yemen as a way to impede Saudi Arabia’s capability to project power to other parts of the region. Iranian officials have cited the Kingdom’s unsuccessful campaign in Yemen as a reason Saudi Arabia would be unable to escalate in Syria, for example.
- The al Houthi-Saleh forces’ positioning on the Red Sea also creates an opportunity for Iran to create or exacerbate disruptive conditions in one of the world's most important maritime chokepoints, as demonstrated by the attacks against the USS Mason.
How has Iran’s regional posture changed since the Saudi-led intervention in Yemen began in March 2015?
Iran has adopted a more aggressive military posture and has expanded its destabilizing regional efforts in the post-nuclear deal environment.
- The IRGC increased its support to the Assad regime in the latter half of 2015 to include the deployment of elements of its own combat brigades to Syria. Iran continues supporting regional proxies, including Lebanese Hezbollah, Iraqi Shi’a militias, and Shi’a networks in Gulf States, in order to expand its regional influence.
- Iran’s Supreme Leader Ayatollah Ali Khamenei departed from the regime’s standard characterization of its military capabilities as solely defensive by calling for Iran to increase its “offensive” capabilities in a speech in late August 2016.
- Iranian officials have made clear that the Islamic Republic will not change its opposition to American and Saudi presence in the Persian Gulf. IRGC officials have explicitly called for the U.S. to withdraw from the Persian Gulf and have vowed to expand Iran’s maritime influence into the Indian Ocean. Iranian naval forces continue to harass American naval ships and personnel.
What is the Iranian regime saying about Yemen?
Iran has provided significant rhetorical support to the al Houthis, including the al Houthi-Saleh faction’s political objectives. It denies providing military support to the al Houthi-Saleh faction.
- On August 3, Iranian Foreign Ministry spokesperson Bahram Ghassemi denied reports from the UK Foreign Office that Iran is sending weapons to Yemen. Ghassemi criticized the claims as “clear interference” in the affairs of Middle Eastern countries and emphasized that Iran’s fundamental policy is creating stability in the region.
- On August 26, Iranian Foreign Minister Mohammad Javad Zarif criticized U.S. Secretary of State John Kerry’s comments about Iranian weapons shipments to Yemen. Zarif claimed that Kerry’s statement “ignores reality” and blamed Saudi Arabia for “war crimes” in Yemen.  Kerry had stated during a news conference in Jeddah that "the threat potentially posed by the shipment of missiles and other sophisticated weapons into Yemen from Iran extends well beyond Yemen."
- On October 5, Iranian Foreign Ministry Spokesman Ghassemi denied a claim from U.S. officials that Iran supplied the al Houthis with the rockets that struck a UAE ship on October 1. Ghassemi added that the U.S. should not make such accusations when U.S. weaponry is “being used to kill thousands of innocent people” in Yemen.
- On October 16, Hojjat ol Eslam Ali Saidi, the Supreme Leader’s representative to the IRGC, denied an IRGC presence in Yemen, noting that the conditions do not require one and there has not been an ask for one. Saidi added, however, that “the people of Yemen and Ansar Allah have the ability to respond to the ruthless crimes of the Saudi regime.”
- On October 16, Senior Military Advisor to the Supreme Leader Maj. Gen. Hassan Firouzabadi denied any Iranian military presence in Yemen. Firouzabadi noted that Iran has only dispatched “medical supplies” to Yemen and “politically supports Yemen’s legal government and people.”
Iran has also signaled support for the al Houthi-Saleh political alliance, which is competing with the Saudi-backed government for legitimacy in Yemen.
- On August 15, Iranian Foreign Ministry Spokesman Bahram Ghassemi announced Iran’s support for an August 13 parliamentary session in Sana’a, Yemen’s capital, held in support of the recently established al Houthi-Saleh governing body, the Supreme Political Council . Hossein Amir Abdollahian, the international affairs advisor to Parliament Speaker Ali Larijani and a former deputy foreign minister, also praised the session as improving Yemen’s cooperation with the world during a meeting with a Yemeni political delegation on August 15.
- On October 14, Iranian Friday prayer leaders criticized American-Saudi cooperation in Yemen a week after a Saudi-led airstrike killed at least 155 individuals in the Yemeni capital of Sana’a. Interim Tehran Friday Prayer Leader Ayatollah Ahmad Khatami criticized the U.S. for supporting “Saudi Arabia’s war against Yemen.”