New Year in the Persian Gulf has opened in the usual atmosphere of scurrility, mistrust and competition. The Iranian nuclear crisis – already animated by economic and cyber warfare, an unrelenting diplomatic offensive, and a systematic program of sabotage, espionage and assassination – has, over the past month, incorporated yet another aspect: the specter of naval confrontation.

Iran is planning a new round of naval war games in February. These follow an earlier round, which unfolded against the backdrop of two unusually bold threats: the first, to close the Strait of Hormuz in response to the imposition of new sanctions; the second, to attack a U.S. aircraft carrier should it return to the Gulf.

Neither threat has so far been acted upon, of course, nor are they likely to be. As a number of analysts have noted, any attempt by Iran to disrupt the passage of oil out of the Gulf would be a largely self-defeating move, given its current economic fragility and abiding dependence on oil exports.

Rather, Iranian bellicosity is better understood as an attempt to shape expectations about its future behavior. In the rough-and-tumble world of international politics, a reputation for recklessness, even irrationality, can be a useful bargaining tool, as North Korean negotiating behavior attests. In particular, Iran is determined to drive up the risks of an attack on its territory, especially its nuclear facilities, by conveying the resolve and ability to respond with naval operations along a spectrum of intensity, from low level harassment of merchant shipping to the kind of hit-and-run attacks on U.S. naval platforms more commonly associated with Chinese strategy in the Western Pacific.

That questions remain about the credibility of these threats is cold comfort for U.S. military planners, though. For them, a preoccupation with capabilities rather than intentions, which can change, means they now confront a potentially asymmetric challenge in the Gulf at a time when they are trying to make deep cuts in the defense budget and reorient their strategic focus to Asia. Indeed, evidence suggests that Washington is taking Tehran’s threats seriously.

This is no surprise. By regional standards, the Iranian navy represents an atypically strong coastal force with a coherent force structure designed not to defeat a superior naval power so much as impose prohibitive costs on intervening in Iran’s southern air and maritime approaches. Built for sea denial, it comprises submarines, mines and fast attack craft armed with anti-ship cruise missiles. Each of these capabilities is cheap relative to the platforms against which they’re being fielded, and each places a disproportionate burden on the side seeking to defend against them. Submarines are hard to find; mines take a long time to clear; and Fast Attack Craft, especially when used in numbers and dispersed formations, are difficult to prevent closing to a range at which their missiles become a serious risk to even well protected ships.

The effects of this force are magnified by congenial naval geography. By contrast with the Western Pacific, with its oceanic expanses and concentric archipelagic chains, the Persian Gulf is a narrow body of water, making it conducive to offensive denial operations. It has one constricted entry point. This creates a funneling effect that allows Iranian forces to concentrate their firepower. Short distances make operations less surveillance intensive, and therefore less technologically demanding. They also compress the warning time available to an enemy defending against missile strikes, while long stretches of noisy coastal water create an ideal acoustic environment for lurking Iranian submarines.

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