Two Australian Hornet fighter planes dropped bombs in the botched coalition air strike that accidentally killed pro-Syrian regime fighters instead of Islamic State terrorists in September, Defence has confirmed.
No single person in the United States-led coalition will be sanctioned for the blunder, which a month-long investigation released on Wednesday morning has instead blamed on failures spread across the operation to ensure key decision-makers had all the information.
Up to 83 irregular pro-Syrian regime forces, who the investigation concluded were not wearing uniforms and were equipped and behaving in a fashion similar to Islamic State fighters, were killed in the strike, in which aircraft from the US, Britain and Denmark also took part.
The Australian Defence Force's Chief of Joint Operations, Vice-Admiral David Johnston, said the investigation had found decision-makers had not been made aware of some caveats in the intelligence-gathering and analysis when they concluded the fighters belonged the Islamic State and should be bombed.
As well as the Hornets, a RAAF E-7 Wedgetail command plane was involved in the operation but did not form part of the decision chain, Vice-Admiral Johnston said. Rather the operation was "under the co-ordination and control of the US combined air operations centre" in the Persian Gulf.
"The decision-makers acted appropriately on the information available to them but there was information in the system that may have caused another judgement to have been formed or at least a pause to say, 'We need to recheck some of these assessments,'" Vice-Admiral Johnston said.
While the command centre is US-run, Australia has personnel embedded there.
Vice-Admiral Johnston said the two RAAF Hornets dropped six GPS-guided, 500-pound bombs out of the total of 37 weapons released by the coalition strike team.
"We're not sure of the extent of damage our bombs caused compared to any of the others but they were all in the broad same target area."
Information-sharing and the processes for confirming so-called "dynamic targets" that pop up while coalition planes are in the air would be improved following the investigation, Vice-Admiral Johnston said.
He said the decision to strike had been based on a drone observation of the troops that had gone on for two days and also several "other technical sources of intelligence".
While he did not say what these were, he indicated they could have included phone signals and satellite images.
"In many ways these forces looked at acted like Daesh fighters … they were not wearing recognisable uniforms or displaying identifying flags or markings."
He said the pro-regime forces had been in a defensive fighting position with vehicles.
The investigation report released on Wednesday morning by the US found that lines of responsibility were blurred. Among other faults, "there was no single individual tasked with fusing this information and presenting the arguments for and against" launching strikes to the key decision-makers.
The process suffered "several breakdowns in the flow of information" and "pieces of information ... did not reach the right decision makers".
Lieutenant-General Jeff Harrigian, the US Air Force commander in the Middle East, said in a statement: "In this instance, we did not rise to the high standard we hold ourselves to, and we must do better than this each and every time."
Vice-Admiral Johnston said that at one point a coalition analyst had said "I'm not sure about this" but his doubts were not taken into account. Also, there were various maps used during the operation that showed different locations of pro-regime forces.
The investigation also found that the coalition gave inaccurate information about the planned location of the operation to Russia, with whom the US liaises to avoid such mistakes, though it was not certain this was decisive, since it is not clear that Russia always knows where pro-regime forces are.
But the probe also laid some blame on Russia, finding that its military officer responsible for liaising with the Americans made an initial call 30 minutes into the operation but after failing to reach his regular contact person did not leave a message and did not call back for another 27 minutes during which a further 15 bombs were dropped.
The strike lasted a total of 59 minutes.
Communication between the US and Russia to avoid mistakes would be improved, Vice-Admiral Johnston said.
The US-led coalition and the Russian-backed Syrian regime are both fighting the Islamic State but are not co-operating with one another in the broader conflict. The coalition has a mandate to target the Islamic State but strictly not to attack the forces of dictator Bashar al-Assad.
A senior RAAF officer who briefed journalists on the investigation said Australian personnel "hold themselves to exceptionally high professional standards" and had found the incident "gut-wrenching".
Vice-Admiral Johnston said the investigation ultimately found that the strikes had been carried out "in full compliance with the rules of engagement and the laws of armed conflict".
"The investigation found that the decisions that identified the targets as Daesh were supported by the information available at the time."
It also found no evidence of "deliberate disregard" of targeting procedures or rules of engagement, he said.
The investigation found evidence of at least 15 deaths but did not dispute other estimates of up to 83 fatalities.