The United States has often struggled to turn rag-tag foreign forces into professional armies, but President Barack Obama is gambling that this time the training effort will succeed in Iraq and Syria.
Eager to avoid sending US combat troops to fight against Islamic State jihadists, Obama is touting a renewed effort to bolster Iraqi government forces and "moderate" opposition fighters in Syria with weapons and advice from seasoned American officers.
But there are doubts in Western capitals that Washington can ensure a rebuilt Iraqi army will not fall prey once again to a Shiite sectarian agenda, or overcome in-fighting and extremism among rival Syrian rebel groups.
Until now, Obama has kept the Syrian civil war -- and its confusing array of rebel factions -- at arm's length, approving only limited support for some "moderate" opposition forces.
That effort, in which a couple of thousand rebels have been reportedly trained by the CIA in Jordan, has been blasted as timid and grossly inadequate by hawks in Washington and Arab allies.
The US president vowed this week to ratchet up support for the rebels, but it remains unclear how much help Washington is ready to provide and whether the West can even identify reliable partners who could form a viable fighting force -- at a time when Islamist hardliners are ascendant.
There are hundreds of rebel groups in Syria, riven by ideological and power rivalries, manned by fighters lacking basic military skills and often dominated by Islamist radicals.
Obama has asked Congress for $500 million to train as many as 5,000 rebel fighters over the next year, using US special forces instead of CIA officers. The plan got a boost this week with Saudi Arabia offering to host the training.
But US lawmakers have been less than enthusiastic, complaining Obama has failed to explain exactly what the plan will involve.
- Islamist or opportunistic -
Senators also insist the US government must find secular-minded rebels to back, though experts who monitor the Syrian conflict say the debate in the United States is "naive."
The issue "is not being discussed at a realistic level," said Aron Lund, editor of Syria in Crisis, a report published by the US-based Carnegie Endowment for International Peace.
Signup to our newsletter and follow us on Facebook and Twitter!
"Most of the insurgency is either opportunistic or Islamist to some extent," he told AFP.
The United States will likely have to demonstrate a pragmatic approach, as it has in the past in Iraq, and accept that it will have to work with rebels with an Islamist bent, according to Lund.
If Washington manages to build a small but well-trained rebel force, backed by US air strikes, it could have a significant effect in Syria, especially over time if the group scores battlefield successes.
"A small group with air support can be quite powerful," Lund said.
US officials say their first challenge is vetting recruits to ensure the program does not backfire and end up delivering weapons to anti-Western extremists or even to IS itself.
Dating back to Vietnam, US attempts to construct professional armies often have faltered, usually because the local leaders see the military as a means of holding on to power rather than defending the country, experts say.
The most recent failure occurred only a few months ago in Iraq, where a massive training effort ended with army divisions throwing down their weapons in a humiliating rout by IS militants.
The outcome, after $24 billion worth of training, came as a crushing disappointment to the US military, but most senior officers blamed the sectarian agenda of former prime minister Nuri al-Maliki, who they say appointed political hacks instead of qualified officers.
"The idea was to create an army that was reflective of the Iraqi society and that model broke down after the Iraqis took command of their own forces and the units started to become aligned in a sectarian manner," said Paul Eaton, a retired US major general who led training efforts in Iraq ten years ago.
- High hopes for new Iraqi government -
With Maliki now out of office, Washington hopes a new government in Baghdad will back an army that represents the whole country's population, including the Sunni community that became alienated under Shiite rule.
"The difference is now we have a new government, a government that has publicly proclaimed a desire to be much more inclusive and responsible," Pentagon press secretary Rear Admiral John Kirby said Thursday.
There are, however, frequent reminders of the Iraqi army's defeats.
Daily updates on the results of US air strikes in Iraq show how American aircraft are regularly blowing up Humvees and other US-made equipment, which was seized by the jihadists in the wake of the Iraqi troops' retreat.