Below the Surface: Iran's Submarine Fleet and the Underwater Dimension of Hormuz
Iran operates submarines in the Strait of Hormuz and the broader Gulf of Oman. The fleet is not large, and the vessels are not modern by the standards of major naval powers. What they represent is a persistent underwater presence in one of the world’s most difficult antisubmarine warfare environments — a shallow, thermally layered, acoustically cluttered body of water where detection is genuinely hard and where even a small submarine with limited capability poses a disproportionate threat to shipping and to surface naval forces.
The most capable units in Iran’s submarine fleet are three Kilo-class boats acquired from Russia in the 1990s. These are conventional diesel-electric submarines that, when properly maintained and operated, can be genuinely quiet in the right acoustic conditions. Kilo-class submarines earned the nickname “Black Hole” from American naval analysts in the Cold War era for their low acoustic signature. The Iranian Kilos have suffered from maintenance problems and limited spare parts availability under sanctions, which has reduced their operational availability and probably their stealth characteristics compared to a well-maintained example. They remain, however, a real antisubmarine warfare problem for any surface force operating in the region.
Supplementing the Kilos is a force of midget submarines — primarily the Ghadir-class, a domestically designed and built vessel capable of launching torpedoes and, potentially, laying mines. These small boats are specifically suited to the shallow-water environment of the Gulf, where their limited diving depth is less of a constraint than it would be in open ocean operations. They can be deployed quickly, are difficult to track in cluttered littoral waters, and can be produced in meaningful numbers given Iran’s domestic shipbuilding capacity. The Ghadir force represents a quantity-over-quality approach that is appropriate for the tactical environment.
The mine-laying potential of both the Kilo and the midget submarine force is the aspect of Iran’s underwater capability that concerns coalition naval planners most. A submarine laying mines at night in the shipping lanes has several important advantages over surface mine-laying vessels: it is harder to detect and intercept, it can operate in areas where surface ships would be exposed to air or surface surveillance, and it can place mines in precise locations that maximize their effect on specific transit lanes. The combination of a credible mine threat with the uncertainty created by underwater presence creates a decision-forcing problem for the commander of any escort or clearing operation.
Coalition antisubmarine warfare assets in the Gulf are substantial. The United States maintains P-8 maritime patrol aircraft, surface combatants equipped with towed array sonars, and helicopter detachments aboard surface ships that are trained for ASW operations. Allied navies contribute additional ASW capability. The challenge is not the capability of the ASW force in isolation — it is conducting effective ASW operations simultaneously with mine countermeasures, tanker escort, surface warfare against fast attack craft, and suppression of shore-based threats. The Gulf is a threat-rich environment, and the underground dimension of that threat environment is the one that imposes the greatest demand on specialized assets.
Iran has invested in domestically designed torpedoes, including rocket-propelled variants that can engage shallow-running targets in confined waters. The development reflects an understanding that commercially purchased weapons systems are subject to sanctions and embargo, and that Iranian underwater warfare capability must be indigenously sustained. The quality of these weapons relative to Western equivalents is lower. Their operational concept — saturation attacks from multiple small submarines in confined waters — reduces the quality differential.
What the submarine force provides strategically is ambiguity. A surface ship in the shipping lane is visible. A submarine is not. The knowledge that Iranian submarines are operating in the Gulf — even if their exact position is unknown — changes the risk calculus for every vessel transiting the strait and for every surface warship operating in the region. That uncertainty is itself a weapon, separate from whatever torpedoes or mines the submarines carry.