Arming insurgencies around the world has rarely worked for the CIA without direct support from Americans on the ground, according to a still-classified agency review of the practice conducted during debate over arming rebels in Syria.

The review, according to The New York Times, was one of many Central Intelligence Agency studies commissioned in 2012 and 2013 as the Obama administration considered how to counter Syrian President Bashar Assad’s forces amid the nation’s civil war.

From aiding contra rebels against Nicaragua’s Sandinista government to the Bay of Pigs invasion in Cuba that ended in disaster, the study concluded that many attempts the spy agency has made in its 67-year history to covertly arm foreign fighters have had little success in effectively turning the outcome of a conflict, especially when there is no American ground support involved.

The study was eventually presented to the White House, where it fueled skepticism among President Barack Obama and top advisers regarding whether to arm scattered rebel groups in Syria.

“One of the things that Obama wanted to know was: Did this ever work?” a former senior Obama administration official involved in the debate told the New York Times. The report, he said, “was pretty dour in its conclusions.”

President Obama made a brief reference to the CIA review earlier this year in an interview with The New Yorker, where he defended his administration against accusations that action taken to arm rebels did not happen fast enough. These allegations have been repeated since then by the likes of Obama’s former Secretary of State Hillary Clinton.

“Very early in this process, I actually asked the CIA to analyze examples of America financing and supplying arms to an insurgency in a country that actually worked out well. And they couldn’t come up with much,” he said.

In the summer of 2012, the administration rejected a plan to arm and train rebel fighters in Jordan. The plan, developed by then-director of the CIA David Petraeus, was eventually reworked. Once it was alleged that President Assad’s forces had used chemical weapons against opposition fighters and civilians, Obama signed a secret order allowing the CIA to train and arm rebels in the conflict.

To this day, the Obama administration has declared rebels they have assisted are so-called “moderates” among such Islamist, Al-Qaeda-associated groups as Nusra Front and the group now known as Islamic State. The latter is the current target of US-led airstrikes in Iraq and Syria to counter the group’s spreading influence in the region.

As the focus of its ire recently shifted from Assad’s Syrian forces to Islamic State, the Obama administration authorized the Pentagon to begin training as many as 5,000 “vetted” rebels per year in Saudi Arabia. The program, though, needs more thorough planning before it begins, the US Department of Defense’s spokesman said last week.

“This is going to be a long-term effort,” said Rear Adm. John Kirby.

The CIA’s review, according to former American officials familiar with its contents, found that the agency has a dismal record when it comes to boosting insurgencies without ground assistance, as is the case right now in the fight against Islamic State. Those efforts include instances like the Bay of Pigs, where the CIA chose to fight proxy wars against the Soviet Union, or to combat Leftists governments, such as the Sandinistas in Nicaragua.

The only instance the review found where an insurgency was successfully armed and trained by the CIA without the help of American ground forces was in Afghanistan in the 1980s, when mujahedeen fighters were assisted against occupying Soviet forces. The covert war there led to the eventual military withdrawal of Soviet troops in 1989. The CIA review also found that the mujahedeen effort received a boost from Pakistani intelligence officers working on the ground with rebels.

Yet looking back, aiding mujahedeen fighters was not a clear-cut victory for the US, as their defeat of Soviet forces eventually led to the rise of the Taliban in Afghanistan, which gave sanctuary to Al-Qaeda in the run-up to their attacks on US territories on Sept. 11, 2001.

“What came afterwards was impossible to eliminate from anyone’s imagination,” said a former senior official about the early debates among Obama administration officials surrounding the arming of Syrian rebels.