For four months now, the Pentagon has trained moderate rebels to wage war in Syria. But as the first group of American-trained fighters sneaked...

For four months now, the Pentagon has trained moderate rebels to wage war in Syria. But as the first group of American-trained fighters sneaked across the border from Turkey, the Al Qaeda-linked Al Nusra Front attacked them.

Despite a series of air strikes, the fate of this contingent–consisting of only 50 to 60 men–isn’t at all clear. But with at least some rebels killed or captured by Al Nusra, the remaining fighters may have simply fled or are otherwise refusing to continue with their mission.

This experience shouldn’t be entirely surprising. The Pentagon lost scores of specially trained agents in Vietnam 50 years ago, too. While the two cases are distinct, Vietnamese operatives dealt with many similar problems in trying to complete their missions.

In the early 1960s, the U.S. and their South Vietnamese allies worked to infiltrate teams into North Vietnam. By 1968, “all teams were judged as probably compromised” by the enemy, according to an official Pentagon study produced two years later.

American commanders in the Pacific later declared the groups to have been a “complete failure in terms of useful intelligence produced,” according to the same report.

In 1964, the U.S. Military Assistance Command, Vietnam–a.k.a. MACV–kicked off the secret mission, commonly known as Operation Plan 34A. The goal was to force authorities in Hanoi to give up their support for communist rebels fighting in South Vietnam through raids, sabotage and psychological warfare.

As part of the larger mission, teams of agents would sneak into the North to gather intelligence, blow up power lines and other infrastructure, spread anti-communist propaganda and–if the opportunity presented itself–foment an uprising.

Three years earlier, the Central Intelligence Agency had already started sneaking the operatives across the border.

When the Pentagon took over the mission, there were more than 20 agents assigned to five teams running around in Uncle Ho’s back yard. These groups operated in strategic locations near the border with Laos, close to the port of Haiphong and just north of the Demilitarized Zone separating the two Vietnams.

To maintain plausible deniability, the South Vietnamese government recruited, employed and paid the agents. However, MACV’s Studies and Observation Group–better known as the Special Operations Group, or just MACV-SOG–vetted and trained these individuals. The Pentagon provided a lump sum to authorities in Saigon to cover salaries.

From the very beginning, the arrangement caused problems. The “inability of STS to recruit high quality individuals for agent training has forced the deployment of mediocre teams,” MACV-SOG officials lamented in a 1964 history, referring to Saigon’s Strategic Technical Service intelligence agency.

Potential agents came from refugee camps and the South Vietnamese military. Saigon also recruited from communist prisoners captured on land and at sea who seemed willing to turn on their comrades.

After putting them through the training courses, American and South Vietnamese forces parachuted the operatives in from special planes, flew them near their destinations on helicopters or sailed them up the coast in junk boats or other ships.

Once in North Vietnam, American handlers encouraged teams–generally fewer than a dozen individuals–to recruit locals to help out. Able to radio back to their handlers, the teams could arrange for supplies and reinforcements to be dropped in when needed. Otherwise, the Pentagon had no direct involvement with the groups on the ground.

Radio messages were the only means to communicate with the agents.

It didn’t take long for the plan to go awry. In the first year of these long-term agent operations, North Vietnamese forces killed all of the members of one group and captured another. Three more teams–codenamed Boone, Buffalo and Lotus–never even got the chance to report in.

Three years later, the Pentagon began to suspect that Hanoi had located and turned the remaining teams against their handlers. North Vietnam could have used the groups to send false information back to the Americans.

“The … program has not been overly successful in terms of intelligence collection, harassment and interdiction,” MACV evaluators concluded in 1968, according to their final study. “The reliability of most intelligence produced … is questionable.”

Still, the operation–eventually codenamed Timberwork–sucked up at least some of Hanoi’s time and resources, causing some level of concern within the regime. But for Washington, which had begun negotiating with North Vietnam, this wasn’t enough of a reason to continue the program.

Instead, MACV-SOG shifted to small reconnaissance teams that would only spend short amounts of time inside North Vietnam, primarily hunting for targets for American bombers. By giving Hanoi less time to sniff out these groups, American officials hoped these so-called Short Term Roadwatch and Target Acquisition teams would be less likely to get killed or captured.

The short-term groups did fare much better than their earlier counterparts. Unfortunately, they often produced equally poor intelligence, and sometimes never reached their targets.

These new operatives were “not supposed to be having contact with anybody,” said Steve Sherman, a former Special Forces soldier and owner of Vietnam-focused publishing house Radix Press. “As long as they didn’t encounter anybody, they were fine.”

While the teams improved over time, Washington steadily lost interest in the war. When Pres. Lyndon Johnson halted the bombing campaign on North Vietnam in the fall of 1968, the agents suddenly had much less to do.

Of course, “there is no available evidence that any team has reported a lucrative target which has been exploited tactically on a real-time basis,” the chief of American operations in the Pacific complained at the time, according to MACV-SOG’s internal review.

“We believe STRATA teams have done as well as could be expected,” MACV officials replied.

Fast forward 50 years later, and the Pentagon seems to be in a similar predicament. The American program to train and equip moderate rebels is having trouble finding suitable candidates. Of course, Syria isn’t North Vietnam. “There are big differences,” Sherman said.

Most importantly, North Vietnam was a tightly-controlled police state, where security services could easily spot interlopers. After more than four years of civil war, the regime in Damascus only controls a limited amount of territory.

In North Vietnam, the agents attempted to hide within the society at large, too. But the Washington-supported rebels in Syria wouldn’t have been trying to insert themselves into Assad’s government or extremist groups such as Al Nursa or Islamic State.

“This is more like inserting an undercover cop into a closed drug cartel,” Gordon Rottman, another Special Forces veteran and military historian, said of the Syria scenario. Rottman pointed out that those groups would have their own vetting process to weed out infiltrators.

Regardless of these distinctions, the performance of the first round of Syrian recruits appears to have been poor, at best. And with no American or coalition troops on the ground, the group was cut off easily from its Western handlers.

For any such program, it’s critical to “have to have some sort of cultural awareness of what’s going on,” Sherman explained. In his opinion, Washington doesn’t seem to have any better understanding of the situation in Syria than it did in Southeast Asia.

“We don’t seem to know enough to know who’s on what side and what side we’re on,” Sherman said.