It’s hard to imagine misplacing billions of dollars worth of weapons. Thousands of assault rifles, mortar rounds, rockets, ammunition and other sophisticated weaponry are not items one would expect simply to go missing or disappear.

But ‘disappear’ they did until their long and shadowy journey from Europe and the United States to their final destination in the hands of terrorists in Syria and Iraq was recently tracked down.

For three years since July 2014 until last month, Conflict Armament Research (CAR) a UK based organisation that monitors the movement of weapons globally, has had its investigators in the field.

Covering an unbroken arc of territory extending from the northern Syrian city of Kobane to the south of the Iraqi capital, Baghdad, the investigators worked forensically, tracking, recovering and logging more than 40,000 items that had made their way into the hands of Islamic State (IS).

In what has been described as the most comprehensive, verified study of IS’s weapons use and supply to date, what CAR discovered is unsettling. For not only did they find that much of the weaponry unearthed originated in shipments that run into the thousands, but it had arrived at its battlefield destinations in Syria and Iraq as a result of what is known as “unauthorised retransfer.”

This is a violation of agreements by which a supplier government prohibits the re-export of materiel by a recipient government without its prior consent.

These non-retransfer clauses are explicitly designed to mitigate the risk of diversion and the subsequent use of weapons by insurgent and terrorist forces to the detriment of international peace and security.

The violation of these clauses runs counter to a range of international and regional counter-diversion agreements, including specific aspects of the Arms Trade Treaty and the EU Common Position on Arms Exports.

But as the CAR research has revealed, weaponry supplied by the United States and Saudi Arabia that originated in European Union (EU) Member States was then passed on to Syrian opposition forces, and ultimately found its way into the hands of Islamist extremists like IS.

“This diverted materiel, recovered from IS forces, comprises exclusively Warsaw Pact-calibre weapons and ammunition, purchased by the United States and Saudi Arabia from European Union (EU) Member States in Eastern Europe,” CAR’s findings concluded.

The details of this convoluted process and the weapons involved are outlined in a newly released CAR report, that has once again throws the spotlight on the murky and controversial workings of international arms transactions.

Entitled 'Weapons of the Islamic State - A three-year investigation in Iraq and Syria' some of the reports findings make for uneasy reading.

Evidence gathered shows for example that far from being old stock, many of IS’s weapons and notably its ammunition, are newly manufactured, having only been delivered to the region since the start of the Syrian conflict in 2011.

It reveals too that many of these same weapons originated in transfers made by external parties, including Saudi Arabia and the United States, to disparate Syrian opposition forces arrayed against the regime of President Bashar al-Assad.

These shipments supplied into Syria through the territories of regional proxies, notably Jordan and Turkey, were rapidly captured by IS forces, only to be turned on international coalition forces by IS fighters.

In plain speak this means that weapons and ammunition supplied by the US most likely were used against US Special Forces and other coalition troops by IS jihadist fighters in battles for cities like Mosul in Iraq and Raqqa in Syria.

These findings are a stark reminder of the contradictions inherent in supplying weapons into armed conflicts in which multiple competing and overlapping non-state armed groups operate.

As defence and security analysts frequently point out, under such circumstances, it is difficult to exert effective control over which groups ultimately gain custody of weapons.

While the Trump administration is said to have ended a secretive CIA operation to arm moderate Syrian rebels battling President al-Assad’s regime, few details on what arms they received were known publicly until CAR’s latest findings.

The group’s comprehensive research has also fully confirmed what other monitoring groups only suspected some time ago. Using a Freedom of Information request, human rights group Amnesty International earlier this year obtained a 2016 US government audit and found that the Department of Defence did not keep accurate records on the location and distribution of weapons supplies sent to Iraq.

“This audit provides a worrying insight into the US Army’s flawed and potentially dangerous system for controlling millions of dollars’ worth of arms transfers to a hugely volatile region,” said Patrick Wilcken, Amnesty’s researcher on international arms control.

In its defence the Pentagon said the Amnesty reports were overblown and that small problems with the inventory system had already been fixed.

“We have a very good system of accounting for equipment and tracking it all the way but it’s never going to be perfect and there are localised inefficiencies,” said Eric Pahon, a Pentagon spokesman, adding at the time that the processes had since been streamlined and some minor inefficiencies fixed following the audit. “We’ve corrected most of these problems with the inventory systems,” Pahon insisted.

But as the latest CAR report makes clear, sending millions of dollars worth of arms into a black hole appear to have backfired on Washington and only ensured a significant source of IS weapons and ammunition.

Overall it is the detail contained in the CAR report that effectively reveals the flaws in US strategy and the extent to which IS benefited militarily on the battlefield.

Documentation CAR obtained illustrates just how quickly these processes of arms diversion can occur following unauthorised retransfer. It highlights the case of one advanced anti-tank guided weapon (ATGW).

Manufactured in the EU, the weapon was then sold to the United States, supplied to a party in the Syrian conflict, and eventually transferred to IS forces in Iraq. The full chain of transactions staggeringly occurring within two months of the weapon’s dispatch from the factory.

Such unauthorised retransfer transactions have allowed IS to obtain substantial quantities of anti-armour ammunition. These weapons which include ATGWs and several varieties of rocket with tandem warheads, are designed to defeat modern tanks and other armour and continue to pose a significant threat to the coalition of troops arrayed against IS forces.

Equally alarming is that almost 40 per cent of all anti-armour rockets used by IS forces in Iraq were produced in the past four years. EU Member States produced nearly 20 per cent of these post-2014-manufactured rockets (and 40 per cent of rockets manufactured since 2010), a fact says the report that sits uncomfortably with the EU’s parallel efforts to degrade the jihadists capacity to wage war and terrorism and to mitigate the wider international effects of the Syrian conflict.

A conventional war requires conventional arms, shells, rockets, grenades, which, as an international pariah, IS could not buy in sufficient quantities. Adding to those that came their way as result of being captured they did something that no terrorist group has ever done before and that they continue to do today: design their own munitions and mass-produce them using advanced manufacturing techniques.

In this capacity IS revealed itself as an organisation with incredible ingenuity when it came to being logistical planners. It moved weapons, munitions and bomb-making materials throughout its war zones on a scale unprecedented for a terror organisation.

As a reporter on the ground those levels of ingenuity and the industrial scale of IS’s own improvised weapons production was brought home to me earlier this year during time spent in and around the then frontline city of Mosul in the company of ordnance disposal experts.

“They even have their own quality control labels,” one Explosive Ordnance Disposal (EOD) expert from the UK based Optima Group told me.

Another expert, Doug Napier, a former US Ranger and infantryman who previously served in Iraq explained how disposal teams have found the most mundane objects set up as Improvised Explosive Device (IED) booby traps. Some even have motion sensors or are fitted with anti-tilt and anti-tamper mechanisms on them so that those trying to render them safe will activate the explosion.

So organised is IS’s production line, Napier says, that he can look at IED parts and recognise when they have come from the same manufactured stock.

“I can look at the parts and tell those that came from the same batches as the taping might be wrapped the same way,” says Napier.

“Then you can tell that on other days they were clearly working from the same instruction sheet but had a different supplies for different components, so there is a lot you can learn just by looking at the bits,” he added.

One of the things highlighted in the latest CAR report is that many of the items that made up shipments that fell into the hand of IS included traceable components and chemical precursors used by the terrorists to manufacture IEDs.

In all secretive American efforts to provide small Syrian rebel groups with weapons munitions and other components have come back to haunt Washington and the CIA once their military largesse found its way into the hands of IS.

What is now apparent from the latest field research is that along with this ready supply, IS developed a system of armaments production of its own that combined research and development, mass production and organised distribution to amplify their staying power and impact. These strategies say some analysts tell us something of what the future might hold in tackling terrorist groups like them.

“It provides a disturbing glimpse of the future of warfare, where dark-web file sharing and 3-D printing mean that any group, anywhere, could start a homegrown arms industry of its own,” says Brian Castner, a former US explosive ordnance disposal officer.

In some of the summary observations in its recent report, CAR points to the fact that IS forces far from being defeated, still possess advanced weapon systems which will pose a threat in the years to come.

They are proficient too it says at manufacturing improvised weapons and IEDs on a large and sophisticated scale and are adept at tapping into regional and international commercial markets to acquire chemical precursors and off -the-shelf products for the development of these weapons.

“Combined with global reach, demonstrated logistical and organisational capacity, and willing recruits around the world, these factors translate into an exportable capacity to conduct insurgency and terrorism well beyond the region,” CAR concluded.

This should give many in Washington food for thought, but will doubtless not hinder the US military and intelligence complex when it comes to supplying arms to perceived allies.

According to the latest figure from the Stockholm International Peace Research Institute (SIPRI), the global trade in arms and military services increased again in 2016, for the first time in five years.

The 100 biggest arms producers accounted for $375 billion in weapons sales in 2016, with US firms having by far the largest share at $217 billion.

In other words the US accounts for roughly 58 per cent of the global arms trade and as the evidence of CAR reveals not only does Washington arm its friends but de-facto its foes as well.