Iran is supporting serious conflicts throughout the region, stretching its limited resources. Moreover, Iran sees Saudi Arabia as one of the chief backers of many of its adversaries. Anything that distracts or wastes Riyadh's resources, Tehran considers a boon. Iran does not control the Houthi and Saleh-aligned forces in Yemen and has little to do with military operations there, though it has had no problem giving some logistical and political support to irritate Saudi Arabia in its own backyard. But the Saudi-led air coalition and naval blockade in support of local ground forces have isolated Yemen and blunted the rapid Houthi and pro-Saleh advances. By building a coalition, Saudi Arabia was able to make progress in Yemen while avoiding a potentially disastrous ground invasion over the mountainous Yemeni terrain against hardened indigenous fighters.
Militarily, it would be impossible for Iran to force open supply lines to Houthi and Saleh ground units. Iran's navy has serious shortcomings in terms of age and capability, especially if it tries to project power beyond the cover of Iran's land and air forces. The Saudi coalition's air forces, meanwhile, enjoy complete air supremacy in Yemen because of their proximity. They would overwhelmingly outmatch any potential Iranian supply attempt. These circumstances raise questions about Tehran's true intention behind deploying unescorted supply ships.
Injecting Political Uncertainty
The answer is likely about advancing an advantageous political narrative. Shaping international opinion can matter. For instance, in 2010 a Turkish nongovernmental organization chartered the Mavi Marmara to be part of the Gaza Freedom Flotilla. Filled with civilians and humanitarian aid, the flotilla attempted to run the Israeli naval blockade, prompting a use of force by Israel Defense Forces that turned violent enough to earn international condemnation and influence Israel's Gaza policies. Similarly, Iran may be trying to provoke a response and to get back into the conversation on Yemen.
One of the criticisms of the Saudi-led military campaign has been the humanitarian crisis generated by casualties, civilian displacements and infrastructure damage caused by the fighting. Yemen already faces potential famine and water stress. Imagine Iranian freighters filled with aid rather than weapons, and Tehran's opportunity to highlight Yemen's plight and bend international opinion becomes clear. Still, the Iranian freighters could contain anything, and military planners from the other side will not be assured until a reputable party can carry out inspections.
Commanders who could be forced to confront the freighters will face many questions. Will the Iranian convoy even approach a blocked Yemeni port? Would the freighters submit to an inspection? If not, does the coalition blockade open fire on unarmed ships? If the freighters do submit to an inspection and are found to be carrying only aid, should Iran be allowed to provide humanitarian support and gain the moral high ground? Or should the ships be turned back while the Saudi-led coalition digs deeper into the moral low ground? In this context it seems that Iran is trying to inject political uncertainty into a conflict that could be turning against its interests.
The U.S. Position
The United States has reacted to these developments by shifting an almost disproportionately large naval force into the region. But overall it is in an awkward position. On one hand, the United States is in nuclear negotiations with Iran and flirting with a broader rapprochement. Iran has also been providing assistance in the fight against the Islamic State in Iraq and Syria. On the other hand, the United States is trying to reassure the Gulf Cooperation Council countries that Washington still has their interests at heart. The deployment of a large U.S. force into the middle of this conflict could be less about a showdown with Iran and more about sitting on top of the belligerents in an effort to keep a relative peace. The last thing the United States needs is further destabilization between states and routes that heavily influence oil and trade in an already unstable region.
Because it is not a serious military option, the Iranian convoy is possibly a political tool. On April 21, Saudi Arabia announced that its current operation, Operation Decisive Storm, was ending and being replaced by Operation Restoration of Hope. This may be the first sign of an opening for negotiations between groups fighting on the ground, but Saudi Arabia has explicitly left all military options on the table, including the continued naval blockade.
Iran still can use this convoy if it advances the country's interests and brings it into a more central role in the conflict or in negotiations. But using the convoy is a gamble as well. With so many warships in an active combat zone, the possibility of miscalculation looms.