Ayn al Issa near Raqqa, Syria (CNN) When Bahoz heard the blasts, he guessed they must have come from French jets. There were 14 of them, all around the time that President Francois Hollande said France had started bombing Raqqa.

The capital of ISIS's self-declared caliphate is eerily close to Bahoz's position. A fighter with the Kurdish YPG units , he sits on a series of outposts along a lengthy earth trench that is essentially the front line with Raqqa -- about 20 miles away, across flat, hostile ground.

"Three days ago we saw 14 airstrikes suddenly hit just nearby, and then the French said they'd started bombing," he told CNN, when we were given rare access to his position near the town of Ayn al Issa.

"We will do our best to avenge Paris ," he vowed.

Raqqa is now firmly in the sights not only of the U.S.-led coalition, but also the French and Russian militaries. And in a few hours along the front line, you can periodically hear distant thuds.

On the day CNN was at the front, they could have come from some of the four Russian missiles activists' group Raqqa is Being Slaughtered Silently reported hit the town, or the four homemade Katyusha rockets they also reported were fired by ISIS.

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The Kurdish fighters here are the defensive line put in place in case a ground invasion begins; there are anti-ISIS militia massing, CNN has repeatedly been told by Kurdish officials with the YPG fighting units, but the operation has yet to begin earnest.

So for now these young men, who say they consider fighting ISIS a duty for humanity rather than a task of vengeance for the friends they have lost, are on the front line in a global battle.

And they have very little in the way of weaponry. Mostly old AK-47s; one fighter told us his used to belong to a friend who died eight months ago.

The terror group down the road

ISIS are just in the next village, visible under a mile away, and regularly fire mortars at one position we visited.

Yet the Kurdish morale is high, lifted by a sense that their fight -- which for months has been about protecting the territory they want to see become a Kurdish homeland called Rojava -- has now taken on an international tone.

"If French, Russian or American fighters come here to fight we will cooperate with them, as we are all fighting to clean the area of ISIS for humanity," one commander there, Sarhad, told us.

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Graffiti on the base walls mocks ISIS leader Abu Bakr al-Baghdadi in a crude caricature, and a plastic skeleton sits at the base entrance, a cigarette in its mouth.

The move towards Raqqa will be difficult, given the open terrain between them and ISIS, but airstrikes will likely assist, if the Kurds ever decide to begin their advance.

Fighting with the YPG is a new alliance called the Syrian Democratic Forces, a collection of Kurdish fighters and other Sunni Arab Syrian armed units.

Many see the alliance as an American idea to try and secure Sunni Arabs as allies for the Kurdish units, so their advance into the predominantly Sunni areas ISIS currently holds is not seen as a land grab by Kurdish forces seeking to create their own homeland.

These forces are the recipients of Pentagon training and equipment and are said to be where the 50 American special forces are applying their training efforts.

A YPG commander in the Syrian Democratic Forces said coordination with the American special forces had begun, but would not confirm their presence in the area.

Where will the manpower come from?

Another commander, one with the Sunni Arab group the Revolutionary Army of Raqqa, said that the preparation for the attack on Raqqa had secured a major victory because many of the local Sunni tribesmen had agreed to rise up against ISIS when the assault began.

The commander, who did not want to be named, said: "We were not expecting this large number to join, but the numbers are now up to 4,000 tribesmen. When we want to move, all of them are ready and we've already managed to sneak weapons to them. We're moving forwards."

CNN could not independently corroborate his claim, but if true it would answer one key question about the assault on Raqqa: where will they get the manpower?

The Kurdish forces are strong and motivated, but lack the numbers and weaponry to take and hold an entire city, and the force that enters that Sunni Arab city will need local Syrian Arab support in order not to be seen as outsiders or risk being rejected by the population.