Elite U.S. Marines arrived in the Libyan capital more than 23 hours after the deadly Sept. 11 assault on a diplomatic mission in the city of Benghazi began, a Pentagon timeline released Friday shows.

A second team tasked with protecting Americans in the besieged eastern city was ultimately not deployed because it would have arrived after all Americans were evacuated, Pentagon officials explained.

The timeline, which added few new substantive details about the government’s response to the two-pronged attack on a U.S. diplomatic compound and the CIA station in Benghazi, appeared to represent an effort by the Pentagon to beat back criticism from Republicans who have suggested the Obama administration could have done more to prevent the death of Ambassador J. Christopher Stevens and three other U.S. employees.

Critics have questioned why fighter planes and gunships weren’t deployed and whether the administration is hiding embarrassing information about what it knew about the threat level in Libya and how it responded to the attack.

Unlike intelligence officials, who released a timeline of their own response and knowledge about the attack a week ago, the Pentagon waited until after Tuesday’s presidential election to offer a detailed timeline of its role in the response.

Documents: Security incidents in Libya since June 2011

A senior defense official who briefed reporters on the chronology said he would speak about the matter only on the condition of anonymity in order to be candid.

“This timeline suggests that DoD took action and took action quickly,” the official said.

The timeline shows that Defense Secretary Leon E. Panetta and senior defense officials learned about the siege on the rudimentary diplomatic outpost less than an hour after it began at 9:42 p.m. in Libya.

Roughly an hour and a half after the attack started, a U.S. unarmed surveillance drone arrived at the site, giving American officials the first live images of the attack.

After midnight, Panetta gave verbal approval to prepare two Marine anti-terrorism teams based in Rota, Spain, for deployments to Benghazi and Tripoli.

One made it to Tripoli, where it reinforced the embassy’s security personnel.

The second platoon was never deployed because all U.S. personnel were evacuated from Benghazi the following morning after an early morning attack on the CIA base in the city.

State Department officials are scheduled to testify about the attack on Benghazi in five closed sessions on Capitol Hill next week, including two alongside intelligence agency officials on Thursday.

The hearings begin Tuesday with one by the Senate Foreign Relations Committee. David H. Petraeus, who resigned Friday as CIA director, had been listed as a witness before the Senate Intelligence Committee.

State Department spokeswoman Victoria Nuland said the hearings are closed at lawmakers’ request. The department’s internal review of the Benghazi attack is expected to be complete next month.

Anne Gearan contributed to this report.