Iranian and U.S. naval forces have had sporadic and occasional hostile encounters since the 1980s. Most encounters – largely by the Islamic Revolutionary Guard Corps (IRCG), not Iran’s regular navy -- involved Iranian harassment of U.S. ships, not live fire. Many encounters have occurred in or near the Strait of Hormuz, through which up to a third of the world’s seaborne oil passes.
“The activities we typically see from the IRGC Navy are not necessarily activities that are directed by the supreme leader or from the Iranian state, rather irresponsible actions by local commanders on the scene, General Kenneth F. McKenzie Jr., the CENTCOM commander, said on April 27, 2021. U.S. military leaders have long warned that the situation in the Gulf can escalate quickly. “I think the big concern here is miscalculation,” General Joseph Votel, then head of U.S. Central Command, told reporters in August 2016.
The most recent incidents were in April and May 2021, when small- and medium-sized Iranian ships harassed larger U.S. warships in the Persian Gulf and the Strait of Hormuz in three separate interactions. The incidents at sea were the first between the United States and Iran in a year. On April 2, three Iranian fast attack boats and one larger vessel swarmed two U.S. Coast Guard ships. And on April 26, a U.S. patrol ship fired warning shots after three Iranian fast attack boats came within 68 yards. U.S. vessels had not fired a warning shot at Iranian ships since July 2017. On May 10, a Coast Guard cutter fired warning shots after 13 Iranian fast attack boats came within 150 yards of six U.S. vessels. The following timeline breaks down the encounters between U.S. and Iranian naval forces in five categories:
The Iran-Iraq War (1980-1988), Iran began targeting commercial shipping in the Persian Gulf two months after Iraq attacked Iran’s oil installation in Kharg Island and several Iranian ships. To protect tankers in the Gulf, the United States launched Operation Nimble Archer (October 1987) and Operation Praying Mantis (April 1988).
The Bush administration: Between 2004 and 2008, Iran carried out at least five provocations of U.S. ships in the Persian Gulf and the Strait of Hormuz. Tensions were high between the United States and Iran after the 2003 U.S. invasion of Iraq, when the Islamic Republic feared it might be next. In 2004, the IRGC captured six British sailors and two British marines who were operating as part of the U.S.-led naval coalition in the Gulf. They were released following negotiations. In December 2007 and January 2008, Iranian vessels harassed U.S. ships in three separate incidents – less than three months after the United States sanctioned the IRGC for supporting Iran’s ballistic missile and nuclear programs. Those incidents happened during the presidency of Mahmoud Ahmadinejad, a hardliner.
During the Obama administration: Between 2008 and 2017, Iranian ships harassed U.S. ships dozens of times in the Persian Gulf and the Strait of Hormuz. Many of the incidents happened during the negotiations that led to 2015 Iran nuclear deal, which was reportedly opposed by some IRGC leaders who did not trust Western powers, especially the United States. In 2015, Iranian vessels engaged in unsafe and/or unprofessional conduct in roughly 10 percent of the 300 run-ins with U.S. ships, or about 30 times, according to U.S. Central Command. Iranian vessels continued to harass U.S. ships after the nuclear deal was implemented in January 2016. In 2016, the United States charged that Iran was responsible for 35 naval encounters deemed unsafe and unprofessional.
During the Trump administration: Between 2017 and 2021, Iranian naval forces harassed U.S. ships at least a dozen times. Tensions with Iran ran high throughout the Trump presidency. National Security Advisor Michael Flynn officially put the Islamic Republic “on notice” on February 1, 2017, three days after Iran had tested a medium-range ballistic missile. Iranian fast boats conducted several provocative maneuvers near U.S. ships during the early months of the administration, but the provocations stopped in August 2017. Iran resumed its harassment of U.S. ships in October 2018—five months after Trump withdrew from the 2015 nuclear deal and reimposed sanctions—but more sporadically than before.
During the Biden administration: As of May 2021, Iranian ships had harassed U.S. ships twice since Biden took office in January 2021. The first incident, on April 2, took place just four days before indirect talks between the United States and Iran on returning to full compliance with the 2015 nuclear deal began in Vienna. The second incident, on April 26, took place during the third round of talks.
The following is a rundown of U.S.-Iran naval encounters originally compiled in 2013 by Michael Connell, principle research scientist at the Center for Naval Analyses (CNA) in Arlington, Virginia, where he directs the Center’s Iranian Studies Program. It has since been updated and edited by Garrett Nada, managing editor of The Iran Primer.
The Iran-Iraq War
May 13, 1984: Iran began attacking neutral shipping in the Persian Gulf in response to repeated Iraqi attacks on Iranian shipping and refining facilities. The tit-for-tat exchanges initiated the so-called Tanker War. The first vessel struck by Iran was the Kuwaiti tanker Umm Casbah. The United States responded by bolstering the capabilities of its Arab allies in the Gulf and increasing its own military presence in the region. Speaker of Parliament Akbar Hashemi Rafsanjani declared, “Either the Persian Gulf will be safe for all or no one.”
July 24, 1987: The United States began to reflag and escort Kuwaiti tankers to protect them from Iranian attacks. Operation Ernest Will was the largest of its kind since World War II. On the first escort mission, the Kuwaiti tanker al Rekkah, reflagged as the MV Bridgeton, struck an Iranian mine, and suffered minor damage.
Sept. 19, 1987: U.S. forces attacked and captured the Iranian logistical vessel Iran Ajr after it was caught dropping mines in the Persian Gulf.
Oct. 19, 1987: U.S. naval forces destroyed two Iranian oil platforms in the Rostam Oil Field. Operation Nimble Archer was in retaliation for an Iranian attack on the MV Sea Island City, a Kuwaiti-owned tanker that had been reflagged as a U.S. ship.
April 14, 1988: The U.S. frigate Samuel B. Roberts, which was escorting tankers in the Gulf, struck an Iranian mine. It suffered extensive damage. U.S. forces retaliated with Operation Praying Mantis, destroying two Iranian oil platforms—both of which were believed to be important Revolutionary Guards Navy staging bases—and disabling or sinking several Iranian regular navy surface assets.
July 3, 1988: The USS Vincennes, a Navy guided missile cruiser, shot down Iran Air Flight 655, a passenger plane flying from Bandar Abbas to Dubai. All 290 of its passengers and crew were killed. According to U.S. officials, the crew of the Vincennes, who were operating in a warzone, mistook the airliner for a hostile Iranian aircraft. Tehran claimed that the downing was deliberate.
During the Bush Administration
June 21, 2004: IRGC naval forces captured six British Royal Navy sailors and two Royal Marines in the disputed Shatt al-Arab, a waterway along the southern boundary between Iran and Iraq. Tehran claimed that the British had strayed into Iranian waters. The captured sailors and marines were released following negotiations. The British personnel had been operating as part of a U.S.-led naval coalition in the Gulf.
Dec. 19, 2007: The USS Whidbey Island reportedly fired warning shots at a small Iranian boat after it approached at a high speed in the Strait of Hormuz.
Dec. 22, 2007: Three small Iranian craft reportedly approached the USS Carr. They turned around after the U.S. ship blasted its whistle to warn them.
Jan. 6, 2008: Five high-speed Revolutionary Guard boats engaged in aggressive maneuvering against three U.S. vessels in the Strait of Hormuz. During the incident, one of the small boats placed what appeared to be small white boxes in the path of the three U.S. vessels. A threatening radio transmission also was heard on a commonly used maritime frequency. It was subsequently determined that the radio transmissions probably came from a third-party heckler, a concept known to mariners as the “Filipino Monkey.”
April 10, 2008: Three small Iranian boats approached the USS Typhoon. One came within 200 yards of the U.S. ship, which fired warning flare. Iran denied U.S. reports on the incident.
April 25, 2008: Two Iranian small boats approached the Western Venture, a U.S.-contracted civilian cargo ship reportedly carrying military cargo to U.S. forces in Kuwait. The Western Venture radioed warnings, fired flares and finally fired warning shots to persuade the Iranians to leave. The incident reportedly occurred about 50 miles off Iran’s coast.
During the Obama Administration
Jan. 6, 2012: Small IRGC boats harassed the USS New Orleans, an amphibious transport ship, while it transited the Strait of Hormuz. On the same day, Iranian boats also harassed the Adak, a U.S. Coast Guard cutter, 75 miles east of Kuwait City. U.S. Navy officials said that the Iranian boats came within several hundred yards of both U.S. vessels. Neither responded to queries or whistles.
Late December 2014: An Iranian patrol aircraft conducted a flyby over the destroyer USS Gridley to warn it to leave an area that the Iranian military was using for an exercise.
March 2015: An Iranian military observation plane flew within 50 yards of an armed U.S. Navy helicopter from the USS Carl Vinson, an aircraft carrier, over the Persian Gulf. The Iranian plane made two passes near the helicopter before flying away.
Late April 2015: A U.S. aircraft carrier and guided missile cruiser were dispatched to the Arabian Sea after an Iranian naval convoy appeared to be headed toward Yemen. The convoy of nine ships was suspected of carrying arms to Houthi rebels, The New York Times reported. By April 24, the Iranian ships had turned away from Yemen. Pentagon officials said that the U.S. ships were sent to reassure Saudi Arabia of U.S. support and to indicate to Iran that the United States would not allow weapons shipments to Houthi rebels in Yemen.
April 28, 2015: An Iranian Navy ship fired shots across the bridge of the Maersk Tigris, a container ship that flew a Marshall Islands flag. The ship was tied to a longstanding legal dispute between the Danish company that had chartered the vessel and an Iranian law firm over containers that had been offloaded in the United Arab Emirates. Iranian personnel then boarded the vessel. (The Republic of the Marshall Islands is a sovereign nation for which the United States has full authority and responsibility for security and defense.) The U.S. Navy based in Bahrain (Navcent) answered a distress call from the Maersk Tigris. Navcent directed a guided-missile destroyer as well as maritime patrol and reconnaissance aircraft to monitor the situation. Iran forced the vessel to go to the Iranian port of Bandar Abbas due. On May 7, Iran released the ship and its crew.
Dec. 26, 2015: An Iranian military vessel fired several unguided rockets toward U.S. military vessels and a French frigate in international waters in the Gulf of Oman, according to U.S. military officials.
Jan. 12, 2016: An unarmed Iranian drone flew toward both the French aircraft carrier Charles de Gaulle and the USS Harry S. Truman while they were in international waters of the Persian Gulf.
Jan. 12-13, 2016: On January 12, Iranian military forces seized two U.S. Navy vessels and held them on Iran’s Farsi Island in the Persian Gulf. Nine men and one woman were aboard the small riverine boats. A variety of human and mechanical errors led to the vessels drifting off course. The sailors were safely released the next day to the U.S. Navy after a flurry of diplomatic contacts.
July 12, 2016: Five IRGC vessels-- four speedboats and a guided-missile patrol ship--came within 500 yards of the USS New Orleans, an amphibious warship hosting General Joseph Votel, the head of the U.S. Central Command, in the Strait of Hormuz. “As you've seen in a relatively compressed space here, there is great opportunity for miscalculations,” Votel told reporters.
Aug. 15, 2016: Seven Iranian naval vessels conducted a military exercise using rockets near the USS Nitze, a guided-missile destroyer, and the USS Tempest, a patrol ship. The rockets were fired within 12,000 yards of the USS Nitze and within 5,000 yards of the USS Tempest. “The vessels were seen firing eight to nine rockets away from the U.S. ships and did not notify them of the intent to conduct a live fire exercise,” said Commander Bill Urban, a spokesman for U.S. Central Command in Bahrain.
Aug. 23, 2016: Four Iranian small boats harassed the USS Nitze in the Strait of Hormuz. The boats approached the USS Nitze at a high speed in an unsafe and unprofessional manner, according to a U.S. defense official. The Nitze fired 10 flares and sounded its whistle several times. The Iranian boats ignored the warnings and U.S. attempts at radio communication. They finally stopped within 300 yards of the U.S. ship.
Aug. 24, 2016: Three IRGC boats crisscrossed the USS Tempest’s bow and “created a possible collision hazard” in the northern Persian Gulf, according to Commander Urban. Later that day, an Iranian patrol vessel approached the USS Tempest head-on despite multiple warnings. The USS Squall eventually fired warning shots.
Later that day, an Iranian Nassar-class boat made a run against the USS Stout, a guided-missile destroyer. The U.S. ship changed course to avoid the Iranian vessel. “These are incidents that carry a risk of escalation, and we don’t desire any kind of escalation,” Pentagon Spokesman Peter Cook told reporters. White House spokesman Josh Earnest said Iran’s motive was unclear, “but the behavior is not acceptable, given that this U.S. ship was in international waters.”
Sept. 4, 2016: Several fast-attack boats operated by the IRGC harassed a U.S. Navy coastal patrol ship. One came within 100 yards of the USS Firebolt and forced it to change course.
Nov. 28, 2016: An IRGC patrol boat trained its weapon on a U.S. Navy Seahawk helicopter. The Navy called the event an “unsafe and unprofessional encounter.” The helicopter was escorting USS Dwight D. Eisenhower, an aircraft carrier, on its way out of the Persian Gulf. “If they continue to test us, we are going to respond, and we are going to protect ourselves and our partners,” warned General Joseph Votel.
Jan. 9, 2017: The USS Mahan, a destroyer, fired warning shots and used radio calls, flares, bells and whistles to signal five Iranian ships to stay away. The ships came within 900 yards of three U.S. vessels that were entering the Strait of Hormuz, according to Pentagon spokesman Capt. Jeff Davis. They eventually left the area after a U.S. helicopter dropped smoke grenades.
During the Trump Administration
March 5, 2017: IRGC fast-attack vessels came within 600 yards of the USS Invincible, a tracking ship, before stopping, forcing the U.S. ship to change course. One Iranian vessel tried to get between the U.S. ship and three British Royal Navy ships, a U.S. official said. An official said that the Iranians did not respond to attempts to communicate over radio.
Mehdi Hashemi, commander of the IRGC’s Zolfaqar Flotilla countered that the U.S. ship was at fault for sailing too close to IRGC vessels. The presence of American and British vessels in the Persian Gulf “endangers the security of this strategic region, which provides a huge portion of the world’s energy,” he said.
March 21, 2017: Two groups of Iranian Navy fast-attack boats harassed a U.S.-led flotilla as it entered the Strait of Hormuz. One of the five vessels, the aircraft carrier George H.W. Bush, dispatched helicopter gunships to hover over the speedboats, which came within 950 yards of the flotilla.
“We had a right to be there as we were exercising freedom of navigation on our way into the Arabian Gulf,” Rear Admiral Kenneth Whitesell told journalists aboard the aircraft Reuters. “They also had weapons uncovered as some of the cameras were able to tell. They had some of the weapons manned. We also have aerial data that they were arming all of these weapons.”
Iran denied that its vessels had harassed U.S. warships. “We emphasize that the Americans would be responsible for any unrest in the Persian Gulf, and again warn that the U.S. military must change its behavior,” said Brigadier General Masoud Jazayeri, the deputy chief of the Iranian armed forces,.
Breaking: Our Navy operates in —yes, correct— the Persian Gulf, not the Gulf of Mexico. Question is what US Navy doing 7,500 miles from home pic.twitter.com/XfDicbWr5s— Javad Zarif (@JZarif) April 26, 2017
April 24, 2017: A U.S. Navy guided-missile destroyer fired a warning flare toward an IRGC vessel that came within 1,100 yards of it. The vessel turned and sailed away. Foreign Minister Mohammad Javad Zarif criticized the U.S. response in a tweet.
June 13, 2017: An Iranian Navy Houdong-class guided-missile boat came within 800 yards of several U.S. vessels, including the amphibious assault ship USS Bataan (LHD-5), the guided-missile destroyer USS Cole (DDG-67) and dry cargo ship USNS Washington Chambers. It initially harassed the formation with shining a spotlight on the destroyer. “Shortly thereafter, the Iranian vessel trained a laser on a CH-53E helicopter that accompanied the formation,” Commander Bill Urban, a spokesman for the U.S. 5th Fleet, told USNI News.
July 25, 2017: The USS Thunderbolt, a patrol ship, fired warning shots near an Iranian vessel that came within 150 yards. The U.S. ship was participating in an exercise with other coalition vessels in international waters, according to Lt. Ian McConnaughey, a spokesman for the 5th Fleet, which is based in Bahrina. He said that U.S. sailors only fired warning shots after the Iranian ship failed to respond to radio calls, flares and horn blasts.
July 29, 2017: The IRGC charged that the USS Nimitz and an accompanying warship dispatched a helicopter and came close IRGC vessels and the Resalat oil and gas platform. “The Americans made a provocative and unprofessional move by issuing a warning and shooting flares at vessels,” the IRGC statement said.
The U.S. military countered that a Navy helicopter saw several IRGC ships, armed with rockets, approaching U.S. ships at a high speed. The helicopter deployed flares after it could not establish communications with the Iranian vessels. The interaction was “safe and professional,” according to the U.S. statement.
Aug. 8, 2017: An Iranian QOM-1 drone came within 100 feet of an F/A-18E Super Hornet jet despite repeated U.S. radio calls to stay clear of flight operations near the USS Nimitz.
Aug. 13, 2017: An Iranian QOM-1/Sadegh-1 drone came within 1,000 feet of U.S. aircraft flying near the USS Nimitz. “The failure of the Iranian UAV to utilize standard, internationally-mandated navigation lights during a night-time approach of a U.S. aircraft carrier engaged in flight operations created a dangerous situation with the potential for collision and is not in keeping with international maritime customs and laws,” Lt. Ian McConnaughey said in a statement.
Jan. 22, 2018: Rear Admiral Mahmoud Mousavi said that Iranian warplanes warned off two “coalition vessels” during military drills in the Gulf. He claimed that the Western ships had approached to monitor Iranian ships.
Late January 2018: U.S. military officials said that Iranian fast boats had not harassed U.S. ships for five months. “I hope it’s because we have messaged our readiness…and that it isn’t tolerable or how professional militaries operate,” General Joseph Votel, the head of CENTCOM, told reporters while traveling in the region.
March 15, 2018: Iranian naval forces had not taken any unsafe or unprofessional actions in the Persian Gulf since August 2017, Commander William Urban, a spokesman for U.S. Central Command, said. “It seems like they’ve absolutely made a conscious decision to give us more space,” he added.
Oct. 26, 2018: Two IRGC fast attack boats shadowed the USS Essex, an amphibious assault ship and the largest U.S. vessel in the Persian Gulf at the time. The boats came within 300 yards of the USS Essex.
Dec. 31, 2018: The USS John C. Stennis was shadowed by some 30 IRGC ships after the aircraft carrier and its strike group entered the Persian Gulf. Photographers and videographers on the Iranian ships filmed the U.S. ships. One small vessel launched a drone that appeared to be taking photographs of the carrier.
July 19, 2019: Six U.S. Navy ships, led by the USS Boxer, were harassed by Iranian ships, a helicopter and a drone after they entered the Strait of Hormuz. An unarmed Iranian Navy Bell 212 helicopter flew alongside the USS Boxer. One Iranian vessel came within 500 yards of the ship. The United States said that the USS Boxer downed an Iranian drone three hours into the encounter, although Tehran denied the report.
April 15, 2020: The United States accused Iranian vessels of harassing six U.S. ships —the USS Lewis B. Puller, the USS Paul Hamilton, the USS Firebolt, the USS Sirocco, the USCGC Wrangell and the USCGC Maui—in the Persian Gulf. Eleven IRGC speedboats reportedly made dangerous and provocative maneuvers near the warships while they were performed training exercises in international waters. Four days later, the IRGC acknowledged the incident but claimed that U.S. forces had violated international maritime laws.
April 22, 2020: President Trump threatened to take military action against Iran if it provoked U.S. forces in the Persian Gulf again. “I have instructed the United States Navy to shoot down and destroy any and all Iranian gunboats if they harass our ships at sea,” he tweeted.
During the Biden Administration
April 2, 2021: Three Iranian fast-attack boats and one ship, the Harth 55, approached two U.S. Coast Guard ships, the Monomy and the Wrangell, in international waters in the southern Persian Gulf. The Harth 55 came within 70 yards of the U.S. ships and repeatedly crossed their front bows. “After approximately three hours of the U.S. issuing warnings and conducting defensive maneuvers, the IRGCN vessels maneuvered away from the U.S. ships and opened distance between them,” the U.S. Navy said. In past incidents, U.S. ships were harassed by smaller Iranian vessels.
April 26, 2021: The USS Firebolt, a patrol ship, fired warning shots after three IRGC fast-attack boats came within 68 yards of it and the USCGC Baranoff, a Coast Guard patrol boat. The incident occurred in international waters of the Persian Gulf. U.S. vessels had not fired a warning shot on Iranian ships since July 2017.
May 10, 2021: The USSCG Maui, a Coast Guard cutter, fired 30 warning shots after 13 IRGC Navy fast boats came within 150 yards of six U.S. military vessels, which were escorting the guided-missile submarine Georgia. Pentagon spokesperson John Kirby said that the number of Iranian boats involved was notably higher than in recent encounters. “This activity is the kind of activity that could lead to somebody getting hurt and could lead to a real miscalculation there in the region, and that doesn’t serve anybody’s interests.” The IRGC denied the U.S. account and said that the warning shots were “provocative.”
Nov. 10, 2021: An Iranian naval helicopter circled the USS Essex in the Gulf of Oman. “There was no impact ultimately to the Essex transit or their operations. But that doesn't mean that this wasn't an unsafe and unprofessional act,” Pentagon Press Secretary John Kirby later said. “Tehran needs to be pressed on why they thought this was a prudent use of their pilots and their aircraft to fly so dangerously close to a U.S. warship.”