He said the U.S. military response helped save lives.
Obama's talk with Panetta
In the months since the attacks, Washington has been a center of debate about how much the State Department had known about threats in the region and whether, after the attacks, the administration tried to mislead the public about its nature.
An independent review released in December lambasted the State Department, saying "systemic failures and leadership and management deficiencies" led to inadequate security at the Benghazi post.
In his remarks, Panetta said the initial reports of the attack were given "almost immediately" to the U.S. Embassy in the Libyan capital of Tripoli.
Within 17 minutes, Panetta said, an unarmed, unmanned surveillance aircraft was dispatched to give U.S. officials a better idea of what was happening. It arrived at the site about 70 minutes after the attack, he said.
Soon, Panetta and Dempsey met with President Barack Obama, the secretary told lawmakers.
Obama ordered that the Defense Department respond to the attack with "all available DOD assets" and try to protect U.S. personnel, Panetta said.
Ayotte and Sen. Lindsey Graham, R-South Carolina asked how many times Obama spoke with Panetta and Dempsey after learning about the attack.
Once, in a half-hour conversation with the president, the men said; Obama did not personally get back in touch with them to ask how the mission to help personnel in Benghazi was going.
"Do you think it's a typical response of the president of the United States to make one phone call, do what you can and never call you back again and ask you, 'How is it going, by the way?'" Graham asked.
Panetta replied, "The president is well-informed about what is going on, make no mistake about it."
"Was any airplane launched in the world before the attack was concluded?" Graham asked.
"If you're talking about a strike aircraft, no, senator," Dempsey said.
"Did anybody leave any base anywhere to go to the aid of the people under attack in Benghazi, Libya, before the attack ended?" Graham asked.
"No," Panetta responded. "Because the attack ended."
Orders without action
But orders to prepare had been given, the defense secretary testified.
Panetta said a Marine security team platoon stationed in Spain was ordered to prepare for deployment while another platoon prepped to head to the embassy in Tripoli. A Special Operations force, then training in Central Europe, was told to prepare to deploy to a staging base in Southern Europe, and another Special Ops force, based in the United States, was told to prepare to move there, too.
"Some have asked why other types of armed aircraft were not dispatched to Benghazi," he said. Armed drones, AC-130 gunships or fixed-wing fighters with the associated tanking, armaments, targeting and support capabilities were not near Libya, and it would have taken at least nine hours to deploy, he said.
"This was, pure and simple, in the absence, as I said -- of any kind of advance warning -- a problem of distance and time," Panetta said.
The quickest response option available was a Tripoli-based security team, he said.
Within hours, Panetta said, that six-person team, including two U.S. military personnel, chartered a plane and flew to Benghazi.
Within 15 minutes of arriving at the annex facility, they came under attack by mortar and rocket-propelled grenades, he said.
Members of the team and others at the annex facility provided emergency medical assistance and supported the evacuation of all personnel.