Costs and Difficulties of Blocking the Strait of Hormuz

To the Editors (William D. O’Neil writes):

Caitlin Talmadge’s analysis of the threat of Iranian action to close the Strait of Hormuz is not only timely but provides many valuable insights.¹ Several aspects of this complex issue call out for further clarification, however.

Costs of Closure

To begin, Talmadge should have put greater emphasis on the costs that Iran would almost surely bear in the wake of any closure attempt. Unless the Iranians were able to convince the world that it was an act essential for self-defense, closure would inflame opinion widely against them. Closing the strait would be seen not only as a serious violation of international norms but, worse yet, one that directly and significantly touched the interests of most states, virtually making it a campaign of piracy. Even states ready to accept Iran’s right to retaliate against some offense would find it hard to forgive a response so indiscriminately damaging.

Under these circumstances, the United States could have wide latitude for action. U.S. leaders might well take the opportunity to leave Iran not only greatly impoverished through a loss of oil revenues and massive destruction of critical infrastructure but stripped of its naval and air defenses. U.S. forces would probably need to seize the Iranian-held islands lying near the shipping lanes east of the strait, and they would not likely be returned. Given the geographic isolation of the region near the strait from the rest of Iran, it is even conceivable that this area might be held under occupation. And the residue of suspicion and resentment against Iran would surely linger among those who suffered losses from the closure, prompting support for a tight sanctions regime.

In short, Iran would find itself essentially in the same position as Iraq after the 1991 Gulf War, if not worse. Such a prospect might sober even the most adventurous or desperate of Iranian leaders.

Figure 1.

Strait of Hormuz and Adjacent Areas

sources: Compiled and drawn by William D. O’Neil, based on bathymetry from “SRTM30 PLUS,” measured and estimated seafloor topography, Scripps Institution of Oceanography, University of California, San Diego, ver. 5.0, last updated September 16, 2008; and land topography from “SRTM 90m Digital Elevation Data,” CGIAR Consortium for Spatial Information, ver. 4, last updated August 19, 2008; supplemented with information from Nautical Chart 62510, published by the U.S. National Geospatial-Intelligence Agency.

The Geographic Situation and Mining

In figure 1, the 25-meter depth contours (the line between the clear and vertically hatched regions) mark the approximate limits of feasible navigation for large tankers.² They are separated by nearly 30 nautical miles in the throat of the strait and fan out slowly for a considerable distance to the west into the Persian Gulf. To the southeast, the Gulf of Oman broadens out rapidly, and water too deep for effective mining is reached quickly. Thus the region from the strait proper westward into the Persian Gulf presents problems distinctly different from those in the Gulf of Oman. Specific shipping lanes are laid out in parts of this region, but there are other waters deep enough to permit passage of large ships if necessary.

Talmadge posits a closure scenario involving minefields to deny transit, with antiship missiles in overwatch. She gives Iran considerable capacity to lay the necessary fields and to sustain a missile threat. In both respects, she exaggerates the seriousness of the threat Iran can pose.

The analogies Talmadge employs to analyze the mining issues have little relevance to this case. The Dardanelles, Wonsan, and Iranian cases she cites were all defensive fields, in waters under the control of the state that laid the fields and not subject to observation by would-be intruders. The Dardanelles case, nearly a century ago, and the Wonsan case, more than fifty years ago, involved dense fields in narrow waters. The Iranians would be attempting to lay offensive fields in broad waters not under their control, and moreover presumably under...