Key point: The Tanker War demonstrated how Iran could retaliate against foreign pressure through calibrated, and semi-deniable attacks on the valuable shipping passing through the narrow waters of the Gulf...

On July 21, 1987, a gigantic 414,000-ton supertanker entered the Persian Gulf with an unusually prominent escort—a U.S. Navy missile cruiser and three frigates.

The narrow straits of the Persian Gulf had become a shooting gallery due to the Iran-Iraq War, still raging seven years after Iraq’s surprise invasion of Iran in 1980. As Iran counterattacked into Iraqi territory, Baghdad—supplied and armed by the Soviet Union, France, Kuwait and Saudi Arabia—began blasting Iranian oil tankers with missiles, often with assistance from U.S. surveillance assets.

Iran retaliated by targeting Kuwaiti tankers with imported Chinese Silkworm missiles. Though terrifying, both side’s anti-ship missiles inflicted relatively little damage as the tankers were simply too bulky to be easily sunk. The same was not true for the frigate USS Stark, struck accidentally by an Iraqi Exocet missile in May 1987 that killed thirty-seven crew.

But Washington had an axe to grind with Tehran, not Baghdad—and decided to respond to pleas for military escort from Kuwait. This led to the controversial policy of reflagging Kuwaiti tankers so they could be escorted by U.S. warships in Operation Earnest Will.

The supertanker Bridgeton—formerly the Kuwaiti tanker al-Rekkah—was the first ship to receive a U.S. escort. Upon entering the narrow Straits of Hormuz, a flight of four Iranian Phantom jets swooped towards the Bridgeton convoy, but turned away at the last minute. On July 23, Tehran rumbled that tanker was carrying “prohibited goods” but made no obvious moves

U.S. intelligence had learned of Iranian plans to attack the convoy with motorboats operated by the Iranian Revolutionary Guard Corps Navy. Indeed, the head of the IRGC had lobbied for such an attack but was vetoed by Supreme Leader Ruhollah Khomeini. He had a subtler approach in mind.

As the Bridgeton cruised eighteen miles west of Iran’s Farsi Island on the morning of July 24, she abruptly struck what resembled a spiked-ball chained to the sea floor—a variant of an old Soviet M-08 mine built by North Korea and exported to Iran. An explosion ripped a large hole the tanker’s port cargo tank, flooding five of her thirty-one compartments but not injuring any crew.

The night before, IRGCN motorboats had lain three chains totaling sixty mines spaced a half-kilometer part along the convoy’s well-known path.

Ironically, the Bridgeton, limping along at just six knots, effectively escorted the U.S. warships back to port, because the huge tanker was the only vessel likely to survive hitting another mine.

The “Bridgeton incident” was an inauspicious start for Earnest Will—highlighting the Navy’s failure to plan for mines. Iranian Mir-Hossein Prime Minister Mousavi gloated it had dealt "an irreparable blow on America's political and military prestige."

Cunningly, the minelaying was both clearly Iranian in origin, while being technically deniable. However, the tactic inspired France and the UK, and later Italy and the Netherlands, to deploy their own warships to the Gulf, including seven minesweepers

The U.S. Navy had few assets immediately at hand to deal with mines. Then, as today, mine warfare was a neglected branch. Weeks later, the Navy deployed the amphibious carrier USS Guadalcanal with RH-53D Sea Stallion minesweeping helicopters aboard. Eventually six ocean-going and five-riverine minesweepers joined Earnest Will, which at its peak involved as many as thirty U.S. Navy ships including carriers and the huge battleship Missouri.

SEALs, Little Birds and Swift Boats

As deploying U.S. mine-sweeping units ashore in Saudi Arabia or Kuwait proved politically prohibitive, Kuwait instead furnished two barges, Hercules and Wimbrown that the Pentagon promptly converted into mobile sea bases, complete with their own extensive self-defense weapons.

The floating bases also hosted assets vital to a covert U.S. counter-offensive called Operation Prime Chance to catch the Iranians red-handed in the act. These included two Navy SEAL teams, six 64-foot-long Mark III “swift boats” and six tiny egg-shaped “Little Bird” helicopters from the Army’s elite 160^th Special Operations Aviation regiment.

On September 21, a trio of Little Bird choppers flying off the frigate Jarrett were assigned to shadow the Iranian tank landing ship Iran Ajr, suspected to have been converted for minelaying. An MH-6 helicopter equipped with a forward-looking infrared (FLIR) sensor and night-vision goggles led the way, escorted by two AH-6 gunships loaded with 7.62-millimeter miniguns and 2.75” rocket pods.

Hovering stealthily 500 meters away, the helicopter crews recorded footage of the Iran Ajr’s crew deploying mines next to the Middle Shoals navigational buoy used by tankers. The Little Birds were ordered to open fire, and they raked the 614-ton vessel with their miniguns, causing the crew to take cover.

However, Iranian sailors resumed deploying the mines a half-hour later. This time the night-vision-aided helicopter pilots unleashed a sustained barrage including rockets, killing three crew—and causing the remaining twenty-six to abandon ship.

The following morning, Navy SEALs on Mark III boats rescued all but two of the Iranian sailors and boarded Iran Ajr. They found nine mines onboard and seized a logbook recording past minelaying activity, including maps showing the locations of those mines. Then the Navy towed Iran Ajr to deep water and blew her up.

A trio of minigun-armed MH-6 helicopters tangled again with four Iranian ships approaching the sea base Hercules on October 8, including a corvette, a Swedish-built Boghammar and two Boston whaler type boats. The Boghammar’s crew fired Stinger missiles at the scout helicopters before being sunk by return fire. Eight Iranian crew were killed, and six more rescued from the water.

When an Iranian missile struck the U.S.-flagged Sea Island City on October 16, injuring eighteen crew, Washington authorized a counterattack three days later called Operation Nimble Archer, resulting in the destruction of two Iranian oil platforms used to host IRGCN boats.

But Iranian minelaying continued. On April 14, 1988, the crew of the frigate Samuel B. Roberts spotted three Iranian mines and realized she had unwittingly cruised into a minefield. While attempting to back out of danger, Roberts struck a mine which nearly split her in two and injured ten sailors. A heroic damage control effort saved the ship and her crew. Navy divers later identified additional mines in the area—with serial numbers identical to those on the Iran Ajr.

Four days later, the U.S. launched a second retaliatory strike targeting two more Iranian oil platforms called Operation Praying Mantis. This time frigates and gunboats of the regular Iranian Navy counter attacked, resulting in the U.S. Navy’s largest foray since World War II, in which half of Iran’s surface combatants were sunk or crippled.

This subdued Iranian naval operations thereafter. The Iran-Iraq war ended four months later—but sadly, not before one final tragic incident. 

On July 3, the U.S. Aegis missile cruiser Vincennes was skirmishing with Iranian fast boats, having unknowingly entered Iranian territorial waters, when her radar reported she was being approached by an Iranian F-14 Tomcat fighter. The cruiser fired two radar-guided SM-2 missiles at the contact—bringing down Iranian A300 airliner Flight 655, killing all 290 civilians aboard.

Operation Earnest Will concluded September 26 when the USS Vandergrift escorted a final tanker into the Persian Gulf. The operatives involved in Prime Chance remained active, however, until June 1990.

The Tanker War demonstrated how Iran could retaliate against foreign pressure through calibrated, and semi-deniable attacks on the valuable shipping passing through the narrow waters of the Gulf—even though the campaign failed to inflict substantial economic damage, or indeed sink many large ships. 

A less violent variant of this strategy has evidently been implemented by Tehran today in its harassment and sabotage of shipping in the Gulf. However, experience from the Tanker War suggested that even controlled, asymmetric harassment attacks may risk provoking a more destructive retaliation.

Sébastien Roblin holds a master’s degree in conflict resolution from Georgetown University and served as a university instructor for the Peace Corps in China. He has also worked in education, editing, and refugee resettlement in France and the United States. He currently writes on security and military history for War Is Boring. This article first appeared earlier in 2019.

Image: Reuters.