WASHINGTON -- The Senate Intelligence Committee on Tuesday released the highly anticipated 500-page summary of its report on the CIA’s post-9/11 torture program, providing a sobering glimpse into one of the darkest chapters in the U.S. government's history.

In the report, a product of a 5-year investigation, Senate investigators reveal sordid details of the systemic and individual failures by the agency personnel who ran the "enhanced interrogation program" -- the government's euphemism for systematic torture -- during the George W. Bush administration. The program involved capturing terrorism suspects and shipping them to secret overseas prisons, where they were subjected to techniques such as waterboarding.

The CIA's program has long been criticized as un-American and a chilling departure from the nation’s values. Opponents allege that it resulted in gross abuses and inhumane treatment of detainees, some of whom were eventually revealed not to have been involved in terror organizations.

The 6,300-page report may be the most unsanitized official account to date of the agency’s program, which the Senate investigators say was mismanaged, poorly conducted and characterized by abuses far more widespread than the CIA previously conveyed to lawmakers.

The newly released document tears apart the CIA's past claims that only a small number of detainees were subjected to the harsh interrogation techniques. The agency has said it held fewer than 100 detainees and subjected fewer than one-third of those to controversial tactics such as waterboarding. But Senate investigators found that the CIA had actually kept 119 detainees in custody, 26 of whom were illegally held. And despite CIA insistence that the program was limited in scope, Senate investigators conclude that the use of torture was much more widespread than previously thought.

The study reveals several gruesome instances of torture by mid-level CIA officers who participated in the program, including threats of sexual violence using a broomstick and the use of "rectal hydration" in instances of harsh interrogations that lasted for days or weeks on end. And, contrary to the agency's prior insistence that only three detainees were subject to waterboarding, the Senate report suggests it was likely used on more detainees.

The report cites the presence of materials typically used for waterboarding being present at certain "blacksites," or secret prisons, where the agency had previously said waterboarding was not used.

Rather than wrestling with the morality of the agency’s torture program or the operation's damaging effect on the U.S.’ international credibility, Senate investigators instead weighed whether the agency's tactics were effective. Through narrative examinations of 20 separate detainee cases, the panel attempted to make the case that the use of harsh interrogation techniques such as waterboarding did not yield valuable intelligence.

"The committee reviewed 20 of the most frequent and prominent examples of purported counterterrorism 'successes' that the CIA has attributed to the use of its enhanced interrogation techniques," Sen. Dianne Feinstein (D-Calif.), chair of the intelligence panel, said in a statement Tuesday. "Each of those examples was found to be wrong in fundamental respects."

In some instances, the study finds, the information acquired proved irrelevant to stopping terror threats. In others, the use of the techniques resulted in detainees providing fabricated or inaccurate information, and in still other cases, the information obtained through interrogating the detainees had already been acquired through other techniques.

Given that the techniques were ineffective, the study says, the agency routinely misled Congress and the White House when it claimed that the use of torture did in fact contribute to intelligence victories. For instance, the Senate report pushes back against the CIA's argument that torture provided the information about Osama bin Laden's courier that helped the U.S. kill the al Qaeda leader in 2011. In a 10-page discussion on the subject, Senate investigators say the information that led the U.S. to bin Laden was obtained from a detainee while he was in foreign custody, prior to being subjected to torture.

The CIA, however, refutes these conclusions. In a roughly 100-page official response released alongside the intelligence panel’s summary, the agency contends that harsh interrogation techniques were effective.

“The sum total of information provided from detainees in CIA custody substantially advanced the Agency’s strategic and tactical understanding of the enemy in ways that continue to inform counterterrorism efforts to this day," the agency said in its rebuttal.

The response argues that it's not clear whether the valuable information could have been acquired by means other than harsh interrogation techniques, although the agency concedes that it's possible.

“It is impossible to imagine how CIA could have achieved the same results in terms of disrupting plots, capturing other terrorists, and degrading al-Qa’ida without any information from detainees, but it is unknowable whether, without enhanced interrogation techniques, CIA or non-CIA interrogators could have acquired the same information from those detainees," the rebuttal said.

Still, the CIA is not advocating a return to the use of torture during interrogations. Rather, it is most concerned with defending itself against charges that it misled Congress and the White House about the extent and value of the program. The official response vehemently challenges the Senate's allegation that the spies acted outside the limits of what the White House had allowed the agency to do. The agency has said that the enhanced interrogations were part of a government-approved program carried out under express orders from within the Bush administration.

"The image portrayed in the Study of an organization that—on an institutional scale—intentionally misled and routinely resisted oversight from the White House, the Congress, the Department of Justice, and its own OIG simply does not comport with the record,“ the agency's response said.

Among the Senate report’s 20 main conclusions are that the CIA misled Congress, the White House and the Department of Justice, that the agency ignored internal critiques of the program, and that the CIA's use of the techniques went far beyond the legal authority bestowed upon it by the Bush White House.

In a statement Tuesday, President Barack Obama said, "The report documents a troubling program involving enhanced interrogation techniques on terrorism suspects in secret facilities outside the United States, and it reinforces my long-held view that these harsh methods were not only inconsistent with our values as nation, they did not serve our broader counterterrorism efforts or our national security interests."

"That is why I will continue to use my authority as President to make sure we never resort to those methods again," Obama added.

"In carrying out that program, we did not always live up to the high standards that we set for ourselves and that the American people expect of us," CIA Director John Brennan said Tuesday in his official response. "As an Agency, we have learned from these mistakes, which is why my predecessors and I have implemented various remedial measures over the years to address institutional deficiencies."

The agency says it has no intention of revamping the current version of its interrogation program, which was curbed as a result of directives from Obama. "It is Director Brennan’s resolute intention to ensure that Agency officers scrupulously adhere to these directives, which the Director fully supports," the statement continued.

"CIA has owned up to these mistakes, learned from them, and taken numerous corrective actions over the years. Further improvements to CIA practices continue to be made today as a result of our review of the SSCI Study," the agency's response noted, referring to the Senate Select Committee on Intelligence, the intelligence panel's full name.

The document’s release marks the conclusion of an explosive, high-stakes feud that played out between the White House’s chief spying agency and its powerful Senate overseers about how much of the report to release publicly.

The feud revolved around the executive branch's insistence that the committee redact the pseudonyms used to identify the mid-level CIA officers involved in the program. Despite a monthslong fight, Feinstein was ultimately forced to relent and allow the pseudonyms to remain blacked out in order to get her study's summary out the door before the panel's incoming Republican majority takes control of the report in January.

The study, which was first commissioned by Feinstein in 2009, began as a bipartisan effort with then-ranking member Sen. Kit Bond (R-Mo.). Republicans on the panel, though, withdrew from the study just months after it was commissioned.

The document released Tuesday will very likely be the only portion the public sees of the Senate Intelligence Committee’s report. Although Feinstein suggested in April that the full report would be released at a later date, Republicans are not likely to seek further declassification once they gain control of the committee, given their opposition to the investigation.

The study set the stage for a dramatic, closed-door dispute between the agency and Feinstein, which resulted in deeply personal jabs and competing referrals to the Justice Department asking for criminal investigations. The CIA accused Feinstein’s staff early this year of taking highly sensitive material from the secure agency facility where the investigation was conducted. Feinstein, meanwhile, insisted the investigators had a right to the document, and further accused the agency of improperly monitoring the computers her staff used to construct the study.

The Department of Justice declined to investigate either the CIA's or Feinstein's allegations. The CIA has since conceded that it did improperly monitor Senate investigators’ computers, and is conducting an independent accountability review board to determine what consequences, if any, its employees should face.