(CNN) -- There was a fiery exchange between Defense Secretary Leon Panetta and Republican Sen. John McCain on Thursday during Panetta's testimony about a deadly attack last September in Libya.
Panetta began his remarks to the Senate Armed Services Committee by saying there was not enough time to fly armed military assets to Benghazi to fend off attackers at the U.S. consulate. Four Americans, including U.S. Ambassador to Libya Chris Stevens, were killed.
Panetta said the response to the attack was "timely and appropriate, but there simply was not enough time given the speed of the attacks for armed U.S. military assets to have made a difference."
McCain, who has constantly lambasted the Obama administration's response to the attack, forcefully challenged Panetta's assertion that the Defense Department did everything it could.
McCain asked why the Defense Department did not send forces based at Souda Bay, Crete, to Benghazi. He said the flight is an hour and a half and that it was "simply false" for Panetta to testify that all resources couldn't reach Libya in time.
"I stand by my testimony," Panetta replied.
McCain testily countered, "Perhaps you can give me some facts."
Panetta then said that contingent was not sent because the State Department didn't request it.
"So it's the State Department's fault," McCain challenged.
Panetta was firm throughout his testimony that there were no "undue delays" in decision making and there was no denial of support from Washington or from the military combatant commanders when the attack happened.
"Quite the contrary: The safe evacuation of all U.S. government personnel from Benghazi 12 hours after the initial attack" and transfer to the Ramstein air base in Germany, "was the result of exceptional U.S. government coordination."
He said the U.S. military response helped save lives.
Panetta's testimony is just the latest in a string of accounts given to congressional intelligence committees, including passionate testimony from former Secretary of State Hillary Clinton.
In the months since the attack, Washington has been on fire with debate about how much the State Department knew about threats in the region and whether the administration attempted to mislead the public about the nature of the attack.
A scathing independent report released in December lambasted the State Department, saying "systemic failures and leadership and management deficiencies" led to inadequate security at the consulate.
In opening remarks, Panetta said he received no imminent threats in the hours leading up to the attack.
He explained that the first reports that an attack was happening were given "almost immediately" to the U.S. Embassy in the Libyan capital of Tripoli.
Within 17 minutes, Panetta said, unarmed, unmanned surveillance aircraft were dispatched for a better idea of what was happening on the ground.
Soon, Panetta and Joint Chiefs Chairman Gen. Martin Dempsey met with President Obama, the secretary explained to lawmakers.
Obama ordered that the Defense Department respond to the attack and try to protect U.S. personnel.
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, training at the time in Central Europe, was told to get ready 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, as well.
"Some have asked why other types of armed aircraft were not dispatched to Benghazi," he testified. Armed UAVs, AC-130 gunships or fixed-wing fighters with the associated tanking, armaments, targeting and support capabilities were not in the vicinity of Libya, and it would have taken at least nine to 12 hours if not more to deploy, he said.
"This was, pure and simple, a problem of distance and time," he said.
The quickest response option available was the Tripoli-based security team, he explained.
Within hours, Panetta said, that six-person team, including two U.S. military personnel, chartered a private airplane and deployed 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 this team, along with others at the annex facility, provided emergency medical assistance and supported the evacuation of all personnel.
All remaining U.S. government employees were safely evacuated from Benghazi, Panetta said.
Panetta said there will "always be tension" between how much security is adequate and how much would create a "bunker-like mentality" at global posts. The answer is not to assign the military to run a "fire house" next to every U.S. diplomatic location.
The military is already financially strapped with a sequester looming for March.
Panetta also said there must be some reliance on host countries to help with security. The attack in Benghazi "raises concerns" about whether that's always possible. Libya's government has been on shaky ground since the end of Libyan leader Muammar Gadhafi's rule.
The defense secretary's testimony comes a few weeks after Clinton told lawmakers that the State Department was moving fast to beef up security at U.S. posts worldwide.
One of the most memorable moments in Clinton's testimony was when she teared up recalling meeting the caskets of Stevens and Tyrone Woods and Glen Doherty, both former Navy SEAL commandos who had been working as diplomatic security officers. The fourth American killed was Sean Smith, an information management officer.
Thursday's hearing occurs as Obama attempts to reorganize his national security team. Some Republicans have been critical of former Sen. Chuck Hagel's nomination to replace Panetta.
But CNN has learned there are now at least five Republican senators who would oppose a filibuster of Hagel, all but ensuring he will be confirmed in the coming days.