On the morning of July 3, 1988, the US Navy cruiser Vincennes was in a gunfight in the Strait of Hormuz. Iranian Revolutionary Guard small boats had fired on its helicopter, and then on Vincennes and the frigate Montgomery.
At 06:47 GMT, Iran Air Flight 655, an Airbus 300, took off from Bandar Abbas, an airport shared by civilian and military aircraft. It was a routine scheduled flight to Dubai, along the commercial airway Amber 59. The cruiser’s radar picked it up 47 nautical miles away and gave it a track number: 4131.
Around 06:50, one of the cruiser’s guns fouled. To bring the other to bear, the ship turned with full rudder at 30 knots and, in the words of the Chairman of the Joint Chiefs of Staff, heeled sharply. At about the same time, an operator’s console showed a momentary Mode II identification signal, a code Iranian F-14 fighters were known to use. The report spread over internal voice circuits, and the contact was entered as an F-14. The Airbus was in fact transmitting the civilian code it had been assigned, Mode III 6760, for its entire flight. The investigation later concluded that the operator’s reading gate had stayed near Bandar Abbas, and that the Mode II signal could have come from a military aircraft on the ground there.
Vincennes broadcast warnings on military and international distress frequencies. None was answered. At 06:51 it told its task force commander it intended to engage at 20 miles unless the aircraft turned away. At 20 miles the captain held fire. The aircraft was climbing through 10,000 feet.
At 15 to 12 miles, the tactical information coordinator began reporting that the altitude was decreasing. By his testimony he reported it at 11 miles, possibly 10, and at 9. The investigation put the time from the first report of descent to the decision to fire at 20 to 30 seconds. At 06:54:05, Captain Rogers gave the order to fire. Two Standard missiles hit the Airbus about 8 nautical miles from the ship, at 13,500 feet. Some 290 people from six nations were on board.
The report’s finding was flat: “At no time did IR 655 actually descend in altitude prior to engagement.” The ship’s command and decision system “showed TN 4131 continuously ascending.” The Aegis system, the Chairman wrote, “performed as designed.”
The commanding officer and his key air warfare operators, the report found, “sincerely believed that they were engaging a hostile aircraft.” To explain the gap between the tapes and what crew members believed they saw, the senior investigating officer asked Navy Medical Corps specialists in combat stress for advice. In their opinion, “Stress, task fixation, and unconscious distortion of data may have played a major role.” After the Mode II report, the coordinator “appears to have distorted data flow in an unconscious attempt to make available evidence fit a preconceived scenario.” They called it “scenario fulfillment.”
The chain of command did not fault the captain. Only seven minutes and five seconds, the Central Command endorsement noted, passed between first detection and the decision to fire. The Chairman judged it unlikely that the descent reports alone “would have settled the issue one way or another given the uncertainties that remained and the extremely short time left,” and wrote that, given what was in the captain’s mind, “there was no other prudent or responsible course.”
He added one lesson. The ship’s senior air warfare coordinators, he wrote, should “confirm or disaffirm important reports (such as descending altitude),” above all the ones that change the picture just as the captain approaches the firing point.