The report says the short-term nature of the mission's staff, many of whom were inexperienced U.S. personnel, "resulted in diminished institutional knowledge, continuity and mission capacity."
Three State Department officials, including two who oversaw security decisions at the diplomatic outpost in Benghazi, resigned in the wake of a review of security failures there, senior State Department officials told CNN Wednesday.
The independent review of the September 11 attacks on the U.S. Consulate in Benghazi released Tuesday cites "systemic failures and leadership and management deficiencies" at the State Department.
The attacks killed four Americans, including Ambassador J. Christopher Stevens.
The failures resulted in a security plan "that was inadequate for Benghazi and grossly inadequate to deal with the attack that took place," the 39-page unclassified version of the report concludes.
Despite all the criticism, the board found no U.S. government employee had engaged in misconduct or ignored responsibilities, and it did not recommend any individual be disciplined.
Eric Boswell, assistant secretary of diplomatic security, and Charlene Lamb, deputy assistant secretary of state for international programs, submitted their resignations, a senior official said. A third official in the Near East Affairs bureau also resigned, the official said.
Boswell and Lamb oversaw security for the Benghazi mission. Lamb testified before Congress about the security precautions. Documents show Lamb denied repeated requests for additional security in Libya.
Sen. John Kerry, who is considered the top prospect for the secretary of state job being vacated by Hillary Clinton, said the State Department "has taken a huge step forward to address the lessons learned from Benghazi."
"It's a dangerous world we're in and I think that this report is going to significantly advance the security interests of those personnel and of our country," Kerry told reporters Wednesday.
Veteran diplomat Thomas Pickering and former Joint Chiefs of Staff Chairman Adm. Mike Mullen, both members of the review board, visited Capitol Hill Wednesday to brief members of the House Foreign Affairs and Senate Foreign Relations committees in private.
"The report makes clear the massive failure of the State Department at all levels, including senior leadership, to take action to protect our government employees abroad," said House Intelligence Committee Chairman Mike Rogers, a Michigan Republican.
A CNN/ORC poll conducted Monday and Tuesday suggests most Americans are dissatisfied with how the Obama administration has handled the aftermath of the attack, but a majority believe that the administration did not attempt to intentionally mislead the American public about that attack.
Only four in 10 Americans believe that the inaccurate statements by administration officials in the days following the Benghazi attack were intended to deliberately mislead the public, while 56% surveyed said they thought those statements reflected what the Obama administration believed at the time had occurred in Libya.
Only 43% said they are satisfied with the way the Obama administration has handled the matter in the past few months; half are dissatisfied.
The review board cited a lack of resources as at least partly to blame for the deaths in Benghazi.
"The solution requires a more serious and sustained commitment from Congress to support State Department needs," it said.
The board found that Washington tended "to overemphasize the positive impact of physical security upgrades ... while generally failing to meet Benghazi's repeated requests" to beef up personnel.
The board completed its investigation this week and sent a copy Monday to Clinton, who said in letters to the heads of those committees that she accepted every one of its 24 recommendations. They include strengthening security, adding fire-safety precautions and improving intelligence collection in high-threat areas.
The report says "there was no protest prior to the attacks," which it described as "unanticipated in their scale and intensity."
It also cites the Bureau of Diplomatic Security staff as "inadequate" in Benghazi on the day of the attacks and in the months and weeks leading up to it, "despite repeated requests from Special Mission Benghazi and Embassy Tripoli for additional staffing."
The report says there had been a "lack of transparency, responsiveness, and leadership at the senior levels" in Washington, Tripoli and Benghazi.
"Security in Benghazi was not recognized and implemented as a 'shared responsibility' by the bureaus in Washington charged with supporting the post, resulting in stove-piped discussions and decisions on policy and security," it says. "That said, Embassy Tripoli did not demonstrate strong and sustained advocacy with Washington for increased security for Special Mission Benghazi."
The mission was also "severely under-resourced with regard to certain needed security equipment," it says.
It singles out for criticism the dependence on "poorly skilled" members of the Libyan February 17 Martyrs' Brigade and unarmed local guards who were supposed to provide security. It noted that, at the time of Stevens' visit, militia members "had stopped accompanying Special Mission vehicle movements in protest over salary and working hours."
Though it said there had been no specific, credible threats on the day of the attack, the significance of the anniversary of the 9/11 terror attacks in 2001 had led Stevens to decide to hold meetings on the compound on September 11 of this year.
But security systems and the Libyan response "fell short" when the compound was penetrated "by dozens of armed attackers."
The report offers a detailed description of what happened that night. It said Libyan mission guards were not present, local militia fled their posts and "there simply was not enough time for armed U.S. military assets to have made a difference."
The board said it could not determine how a gate at the compound was breached, "but the speed with which attackers entered raised the possibility" that the guards had left it open.
Clinton, who is recovering from a stomach virus and concussion, ordered the review in the aftermath of the attack. Such reports are mandated by Congress when Americans working on behalf of the U.S. government are killed overseas.
A notice sent to State Department employees said the implementation team had met Tuesday and would continue to do so regularly to carry out the board's recommendations.
The politics surrounding the events that led to the report have claimed one political casualty, with Susan Rice, U.S. ambassador to the United Nations, last week pulling her name from consideration to succeed Clinton. Some Republican senators had said they would put a hold on her nomination if President Barack Obama had submitted it, based on comments Rice made in the days after the attack.
In place of Clinton, Deputy Secretaries of State William Burns and Thomas Nides will testify before the House and Senate committees Thursday.
CNN's Adam Levine an Elise Labott contributed to this report.