On 3 July 1988, Iran Air Flight 655 — a regularly scheduled service between Tehran, Iran and Dubai, UAE — departed from its mid-flight stopover at Bandar Abbas Airport near the Persian Gulf. The Airbus A300 was shot down by an SM-2MR surface-to-air missile launched from U.S. Naval cruiser the USS Vincennes seven minutes into what was expected to be a expected 28 minute flight over the Gulf, which had mistaken it for an Iranian F-14 Tomcat. All 290 people aboard were killed.

The event happened during the heightened geopolitical tensions in the Persian Gulf caused by the Iran-Iraq war, when the Iranian government had been stopping boats in the Gulf they suspected of doing business with Iraq. At the time Flight 655 took off from Bandar Abbass Airport, the USS Vincennes and another Naval cruiser — the USS Montgomery — were engaged in action with several Iranian gunboats, a 19 August 1988 Department of Defense investigation into the incident reported:

On the morning of 3 July, Montgomery observed seven [Iranian Revolutionary Guard Corps, IRGC] small boats approaching a Pakistani vessel. The number shortly thereafter grew to 13 and they began to challenge nearby merchantmen. Vincennes was ordered to the area to support Montgomery and launched a helicopter to reconnoiter the scene. In the process the helicopter was fired upon. Vincennes and Montgomery closed the general areas of the small boats. Two of the boats turned toward Vincennes and Montgomery while the others began to maneuver erratically. These actions were interpreted as manifesting hostile intent and both ships, after being given permission, engaged.

It was in this context, the report stated, that the Vincennes radar noted the Airbus A300 taking off from Bandar Abbass Airport (which has both civilian and military uses), and therefore the crew thought it was related to the hostilities in which they were already engaged:

This action, involving high speed course changes and gunfire at close range, was still In progress when [Flight 655] took off from the Joint military/civilian airfield at Bandar Abbas and headed toward Dubai. It is hard to overemphasize the fact that Bandar Abbas is also a military airfield. The Air Bus was probably not informed of the surface action taking place in the Strait. Informed or not, Flight 655 logically appeared to have a direct relationship to the ongoing surface engagement.

The Department of Defense report noted that Bandar Abbass was the same airfield from which Iran had launched F-4s in support of an attack on U.S. naval forces earlier that year, and from which Iran had repeatedly launched F-14 fighter aircraft the week before.

According to the crew of the Vincennes, there were other reasons to believe that the plane was on an attack path, though the bulk of those claims have been proven inaccurate by later investigations. On 4 July 1988, the day after the incident, president Ronald Reagan articulated the primary reasons in a statement to the press:

Reagan, who was spending the Fourth of July holiday at Camp David, said the Iranian aircraft “was headed directly for the Vincennes” and had “failed to heed repeated warnings.” The cruiser, he said, fired “to protect itself against possible attack.”

The notion that the flight was “headed directly for the Vincennes” comes from crew testimony suggesting the plane was descending, as an attacking plane would, as it approached the area of their ship. Records automatically collected by the ship’s Aegis Combat System, however, later demonstrated that the radar on the Vincennes indicated it had been climbing, not descending — something described by the Department of Defense investigation as “the most puzzling mistake.”

Communication issues also complicated efforts to distinguish the passenger plane from a fighter jet. Crew members aboard the Vincennes recall that the signal from the airbus was “squawking” — an aviation term for a signal broadcast by planes to identify themselves — on “Mode II,” which is used only for military planes. Records from the ships Aegis system, however, indicate that this was not the case:

We know from the tapes that nine of the consoles in the command information center were monitoring the airliner. Every one showed a Mode III — used by both military and civilian aircraft — coming from the approaching plane. No consoles showed a Mode II squawk. But that’s not what the crew recalls.

The crew of the Vincennes also attempted to contact the plane on a variety of radio frequencies, and never heard a response — something they felt indicated an aggressive posture as well. According to reports, the Vincennes attempted to contact the pilot of the Iran Air flight four times on military emergency frequency and three times on a civilian emergency frequency. Notably, the crew did not use the air traffic control frequencies to which a civilian plane would have been most responsive.

The 1988 Department of Defense investigation — known as the Fogarty Report — noted these errors, but declined to assign blame to the ship’s commanding officer and crew:

It is my view that, understanding the entire context, reasonable minds will conclude that the Commanding Officer did what his nation expected of him in the defense of his ship and crew. This regrettable accident, a by-product of the Iran-Iraq war, was not the result of culpable conduct onboard Vincennes.

The Iranian government does not accept the explanation that this was an accident, and instead contends that the United States government performed an intentional and unlawful act while in Iranian waters:

The U.S. Navy did “hanker” for a chance to experiment with its new weapons. To do so against a civilian airliner thereby murdering 290 innocent people was not only irresponsible and illegal; it was unconscionable.

In April 1990, two top officers on the USS Vincennes during the Flight 655 accident were awarded medals for “meritorious service,” though they were given in spite of — not because of — the Iran Air incident:

Navy officials said this week that while [Capt. Will Rogers III] and some of his officers made mistakes in connection with the shooting, the commendations were awarded for their “contributions to the USS Vincennes over their entire tour on board.

In 1996, the United States government reached a settlement with both Iran and the International Court of Justice:

The United States shall pay the Settlement Amount of US $131,800,000 [and] shall include US $61,800,000 … for the heirs and legatees of the 248 Iranian victims of the aerial incident … Upon payment of the Settlement Amount and issuance of the Order of Discontinuance by the Court, Iran shall indemnify and hold harmless the United States and its affiliates, subsidiaries, agents, agencies, instrumentalities, predecessors, successors and assigns against any claim, counterclaim, action or proceeding that Iran, its affiliates, subsidiaries, agents, agencies, instrumentalities, predecessors, successors and assigns may raise, assert, initiate or take against the United States with respect to, arising out of, in connection with or related to the I.C.J. Case.

While the United States has described the incident as “a terrible human tragedy” and has “expressed deep regret over the loss of lives caused by the incident,” it has never formally apologized.