* First military reaction was 17 minutes into attack
* Panetta alerted about an hour into the attack
* CIA team evacuated consulate as Pentagon began troop moves
Pentagon leaders knew of the Sept. 11 attack on the U.S. Consulate in Benghazi an hour after it began, but were unable to mobilize reinforcements based in Europe in time to prevent the death of the U.S. ambassador, according to a timeline released on Friday.
Senior defense officials, speaking on condition of anonymity, rejected criticism accusing the Pentagon of failing to move quickly to send reinforcements to relieve the consulate or using armed aerial drones to fire on the attackers.
"The Department of Defense acted quickly after learning of the incidents unfolding in Benghazi," said one official, adding that Marines, special forces and other military assets had either been employed or put in motion during the attack.
"Unfortunately, no alternative or additional aircraft options were available within a timeline to be effective," the official added.
The Obama administration's response to the attack became a highly charged political issue in the last weeks of the presidential campaign. The CIA, which had a base near the consulate, and the State Department have released timelines on the incident.
According to the Pentagon's timeline, the military's Africa Command, based in Europe, ordered an unmanned, unarmed surveillance drone diverted to the city in eastern Libya just 17 minutes after the attack on the consulate began about 9:42 p.m. local time (3:42 p.m. EDT), the first military action in response to the incident. It took the drone more than an hour to arrive at the scene.
Defense Secretary Leon Panetta's office was notified of the attack 50 minutes after it began, and Panetta learned of it shortly thereafter as he and the military's top general headed to a previously scheduled meeting with President Barack Obama at the White House.
Obama, Panetta and Army General Martin Dempsey, the chairman of the Joint Chiefs of Staff, discussed potential responses to the unfolding events in Benghazi during their meeting, which began 78 minutes after the start of the Libya attack, according to the timeline.
Panetta and Dempsey then returned to the Pentagon and began a two-hour series of meetings with General Carter Ham, head of Africa Command, and other senior military leaders from 6 p.m. to 8 p.m. EDT (12 a.m. to 2 a.m. Libya time) to organize responses to the attack.
But as they arrived at the Pentagon, the surviving personnel from the consulate in Benghazi were being evacuated by a CIA team that arrived from a nearby base, about two hours after the start of the attack. Ambassador Christopher Stevens was missing.
Stevens' body was found at a local hospital. He apparently died of asphyxiation in the smoke-filled diplomatic compound after it was set ablaze by the attackers. Stevens and three other U.S. personnel died in the attack on the consulate and a nearby CIA annex.
"When initial reports came in, we knew the ambassador could not be reached," a senior defense official told reporters. "We were looking at the possibility of a potential hostage-rescue scenario, for instance. So we didn't know if this was going to be an hours-long event or a days-long even or longer."
During the meetings, the group formulated a response to the attack and gave verbal orders to prepare to deploy two teams of Marine anti-terrorism troops, used for providing security, and two special forces units, one based in Europe and the other in the United States.
One Marine Corps Fleet Antiterrorism Security Team, or FAST team, was designated for the U.S. Embassy in Tripoli and the other for the consulate in Benghazi. The special forces units were ordered to prepare to go to a staging base in Europe.
As the Pentagon meetings got under way, a six-man security team from the embassy in Tripoli, which included two Defense Department personnel, left for Benghazi, landing at the airport at 1:30 a.m Libya time (7:30 p.m. EDT).
A CIA timeline released last week said that team was held up at the airport trying to organize transportation and locate the missing U.S. ambassador.
The team from Tripoli got to the CIA base in Benghazi, at about 5:15 a.m. Libya time (11:15 p.m. EDT), arriving at the start of a mortar attack by militants that killed two U.S. security officers.
An hour after that, a Libyan military unit arrived at the CIA base and helped evacuate all U.S. personnel and the bodies of Stevens and the other slain Americans.