Iran threatened to close the Strait of Hormuz last week, in response to U.S. and European Union moves to apply sanctions on its oil industry. Only 21 miles wide at its narrowest point, the strait sees the passage of roughly 28 tanker ships a day, half loaded, half empty. Some 17 million barrels of oil—20% of oil traded in the world—go through this chokepoint. If Iran really could close the strait, it would do great damage to the world economy. But it would also damage its own already shaky economy because Iran relies on the strait to deliver oil exports to China and other customers.
In any case, closing the strait is not nearly as easy as Adm. Habibollah Sayari, commander of the Iranian Navy, would have it. He said that closing the strait is "as easy as drinking a glass of water." Actually it would be about as easy as drinking an entire bucket of water in one gulp.
Iran tried this trick before and failed miserably. In 1984, during the Iran-Iraq War, Saddam Hussein attacked Iranian oil tankers and the Iranian oil-processing facility at Kharq Island. Iran struck back by attacking Kuwaiti tankers carrying Iraqi crude and then other tankers in the Persian Gulf. In 1987, after years of growing disruptions in this vital waterway, President Ronald Reagan responded by offering to reflag Kuwaiti tankers with the U.S. flag and provide U.S. naval escort. Iran shied away from direct attacks on U.S. warships but continued sowing mines, staging attacks with small patrol boats, and firing a variety of missiles at tankers.
On April 14, 1988, the guided-missile frigate USS Samuel B. Roberts struck an Iranian mine; no sailors were killed but several were injured and the ship nearly sank. The U.S. Navy responded by launching Operation Praying Mantis, its biggest surface combat action since World War II.
Half a dozen U.S. warships in two separate Surface Action Groups moved in to destroy two Iranian oil platforms. The Iranians responded by sending armed speedboats, frigates and F-4 aircraft to fire at the U.S. warships.
In defending themselves, the American vessels sank at least three Iranian speedboats, one gunboat and one frigate; other Iranian ships and aircraft were damaged. The only major U.S. loss occurred when a Marine Corps Sea Cobra helicopter crashed, apparently by accident, killing two crewmen.
The war all but ended less than three months later when the guided missile cruiser USS Vincennes mistakenly fired a surface-to-air missile at an Iranian passenger airliner that it had mistaken for a fighter jet. The plane was destroyed and 290 people killed. Although this was an accident, the Iranian regime was convinced that Washington was escalating the conflict and decided to reach a truce with Iraq.
The greatest loss suffered by U.S. forces during this whole conflict occurred in 1987 when an Iraqi aircraft fired an Exocet missile that hit the frigate USS Stark, killing 37 sailors and injuring 21. (Saddam Hussein claimed this was an accident.)
The Iranians had little to show for their efforts: Lloyd's of London estimated that the Tanker War resulted in damage to 546 commercial vessels and the deaths of 430 civilian mariners but many of those losses were caused by Iraq, not Iran. While these attacks temporarily disrupted the free passage of oil, they did not come close to closing the strait.
Despite the unveiling of a new antiship cruise missile called the Qader, Iran's conventional naval and air forces—on display during the Veleyat 90 naval exercises in the Persian Gulf which ended Monday— are still no match for the U.S. and its allies in the region. The U.S. alone has in the area two carrier strike groups, an expeditionary strike force (centered around an amphibious assault ship that is in essence a small aircraft carrier), and numerous land-based aircraft at bases such as Al Udied in Qatar, Al Dafra in the United Arab Emirates, and Isa Air Base in Bahrain. The U.S. and our Arab allies (which are equipped with a growing array of modern American-made equipment such as F-15s and F-16s) could use overwhelming force to destroy Iran's conventional naval forces in very short order.
Iran's real ability to disrupt the flow of oil lies in its asymmetric war-fighting capacity. Iran has thousands of mines(and any ship that can carry a mine is by definition a mine-layer), a small number of midget submarines, thousands of small watercraft that could be used in swarm attacks, and antiship cruise missiles. If the Iranians lay mines, it will take a significant amount of time to clear them. It took several months to clear all mines after the Tanker War, but a much shorter period to clear safe passages through the Persian Gulf to and from oil shipping terminals.
Antiship cruise missiles are mobile, yet those can also be found and destroyed. Yono submarines are short-duration threats—they eventually have to come to port for resupply, and when they do they will be sitting ducks. U.S. forces may take losses, as they did with the hits on the USS Stark and Samuel B. Roberts, but they will prevail and in fairly short order.
The Iranians must realize that the balance of forces does not lie in their favor. By initiating hostilities they risk American retaliation against their most prized assets—their covert nuclear-weapons program. The odds are good, then, that the Iranians will not follow through on their saber-rattling threats.
But this heated rhetoric does suggest how worried the Iranians are about the potential impact of fresh sanctions on their oil industry. All the more reason for the Europeans to proceed with those sanctions.
Mr. Russell, a navy captain, is a visiting fellow at the Council on Foreign Relations. In 2010-2011 he was chief of staff to U.S. Navy Central Command/Fifth Fleet in Bahrain. Mr. Boot is a senior fellow in national security studies at the council.