Iran’s covert operations chief Qassem Soleimani is back in Syria and beaming for the cameras, according to photos of the selfie-prone Quds Force commander released this week. But it’s not all smiles for the troops in Syria under his command.

Iran has now become the ground army fighting to save its embattled ally Bashar al-Assad, while Russia has become his air force. And while two conventional militaries ranged, by land and by air, against a consortium of insurgencies ought to be faring well, in the last month, Iran’s Revolutionary Guards have been hemorrhaging casualties. So far, they’ve lost third lieutenants all the way up to generals—and the deaths are starting to pull back the curtain on just whose boots are on the ground in Syria.

The Quds Force, the covert operations arm of Iran’s Islamic Revolutionary Guard Corps (IRGC), has been in charge of Iranian support for the Assad regime since the very beginning. And it has lost men over the years as the protests against the regime escalated into full scale civil war.

But now the conflict has entered a new phase as an offensive jointly planned by Russia and Quds Force chief Soleimani is taking hold. Iran is adding more “advisors” to its presence in Syria—which numbers nearly 2,000 strong according to Joint Chiefs Chairman Gen. Joseph Dunford—and leveraging Russian airstrikes to try and recapture territory around Aleppo. Estimates of Iran’s death toll since the Aleppo offensive kicked off in mid-October vary, but some have placed the butcher’s bill at over 40 dead in roughly a month, with news of new casualties every week.

And it’s from the announcements of these deaths in the Iranian media that the composition of the IRGC’s presence in Iran is coming into greater focus. The Guards have sent troops with a diverse set of IRGC unit backgrounds, suggesting that Iran is drawing on a broad range of skills and capabilities to prop up the Assad regime’s military.

“If you listen to what the IRGC says they’re doing, they say they’re assisting the Syrian military and the [National Defense Forces militias] at various different levels in how to run hardware, to use artillery, to do tactics and logistics—everything from the tactical to the strategic,” says Afshon Ostovar, an Iran expert at the Center for Naval Analyses, a federally funded research and development center.

“It doesn’t make sense for [Quds Force] to be able to advise on everything,” says Ostovar. “You’re going to need various skills brought to bear and it doesn’t make sense to just bring your special forces Quds Force guys, who are trained in language, tradecraft and bomb-making, to teach a guy how to use a howitzer or how to integrate armor with infantry tactics.”

The presence of IRGC personnel with skills outside the Quds Force’s usual cloak-and-dagger operations is evident in the deaths of veterans of the IRGC’s 8th Najaf Ashraf Armored Division in Syria, a unit well suited to operate and advise on Syrian military equipment. The 8th Armored Division “operates Soviet-origin T-55 and T-72 tanks, BMP-2 infantry fighting vehicles, and 2S1 self-propelled artillery, equipment which also form the backbone of Syrian armored units,” according to Galen Wright, an associate researcher at Armament Research Services.

According to recent casualty announcements in Iranian media, nine soldiers from the 8th have been killed in Syria since 2013, with five deaths spanning a 10-day period from October into November—a distinction which means it has “allocated the highest number of martyrs to the defense” of the Assad regime, according to Iran’s Isfahan Metropolis News Agency.

Iran generally explains that their troops are present in Syria only to advise, brushing off reports that they participate directly in combat operations (although that pretense sometimes slips). But the deaths of Shia militia members in Syria like Liwa Fatemiyoun belies the notion of a purely advisory IRGC presence.

Liwa Fatemiyoun is one of a number of Iranian-backed militias in Syria, suffering casualties including the loss of a brigadier general. It’s comprised of Afghan Shia, many of whom are refugees living in Iran, and has helped offset manpower problems from within Syria’s own forces.

The Fatemiyoun “are a subunit of IRGC Quds Force for external operations,” says Phillip Smyth, a researcher at the University of Maryland’s Laboratory for Computational Cultural Dynamics who specializes in Shia militants and has studied Liwa Fatemiyoun. “They appear to be under Quds Force command. They also have Quds Force aides and commanders that are going with them to the front, not always Afghan. So it’s quite clear this is a foreign legion of sorts for them.”

Iran sent an experienced senior officer to help prop up Syria’s homegrown militia networks, in addition to exporting its own. In October the IRGC’s Brig. Gen. Hossein Hamadani was killed in northern Syria. His background as the man in charge of organizing IRGC’s Basij paramilitaries during the crackdown against protesters in Tehran following the 2009 presidential election there made him a logical choice for the job of training Syrian irregulars for the defense of the Assad regime. IRGC chief Maj. Gen. Mohammad Ali Jafari eulogized Hamadani by saying he managed to convince Syrian President Bashar al-Assad “of the importance of organizing people as the only way to save Syria.”

With the presence of senior officers have come troops from Ansar al-Mahdi, an IRGC organization tasked with the protection of senior government officials. The unit, which has also protected Iranian nuclear scientists in the wake of an assassination campaign, is part of the IRGC’s Protection and Security Organization alongside the Supreme Leader’s Vali-ye Amr Security Unit praetorian, explains Marie Donovan, an Iran expert at the American Enterprise Institute. At least two officers from Ansar al-Mahdi have died in Syria so far, Amin Karimi and Abdollah Baqeri Niyaraki, a former bodyguard to then-President Mahmoud Ahmadinejad.

“I think that the two Ansar al Mahdi Security Unit members were probably just doing their jobs protecting senior officials when they were killed,” says Donovan. “A lot of senior officials—including [Hamedani]—have been making many trips between Iran and Syria.”

Special operators from the Saberin commandos of the IRGC Ground Force have also shown up among the dead in Syria. Iranian media has identified four members of the Saberin killed in Syria since October, including a colonel from the unit. Photos of two more soldiers killed in Syria, Ruhollah Emadi and Sajjad Tahernia, show the men wearing Saberin patches on their uniform. Tahernia can also be seen wearing the rank insignia of an IRGC staff sergeant, suggesting that the Guards’ presence in Syria may not be exclusively restricted to officers.

Saberin units have “limited special operations capabilities” and are attached to each IRGC provincial corps in Iran with tours combating domestic insurgents from the Kurdish PJAK and Sunni Islamist Jundullah, according to an unclassified 2010 Defense Department report. But Syria would not be their only foreign deployment as Iranian media has reported the death of a Saberin commando in Iraq fighting the Islamic State.

The spectrum of service backgrounds of the IRGC dead in Syria reflects not just a range of skills but different generations of IRGC wartime experiences, from the grueling trench warfare of the Iran-Iraq war to more recent counterinsurgency campaigns at home and covert support to insurgencies in the Middle East.

It’s hard to say whether those skills and experiences will translate to success on the battlefield for Syria. Thus far, Russian airpower and Iranian ground forces have helped the Assad regime claw back some patches of territory in the course of offensives around Aleppo, notably along the road linking managed to claw back some territory in their offensives around Aleppo, most recently. But Syria’s brutal war has seen advances and reversals as the conflict has dragged on over the past four years.

“I think they’re learning on their feet,” Ostovar says of Iranian forces in Syria. “The IRGC is certainly going to come out of this far more prepared for warfare with anybody else in the future than they were going into it. This is practice and they’re getting a lot of it you would think. They’re certainly dying.”