DW: Your teams were able to gather firsthand information at no less than six weapons manufacturing facilities close to the Iraqi city of Mosul. What kind of weapons were produced, at what scale and in what quality?

James Beavan: They were producing primarily improvised mortar bombs of various calibers but mostly 120 mm. At least two types of rockets and in terms of production by looking at what they were manufacturing at the factories alone and also what we recovered on the battle field, they are running in the tens of thousands. In terms of quality, they issue standardized quality control measures, so we were able to recover documents which list the precise specifications and when we measured the ammunition itself, we found that it conformed exactly to the specifications. So the precision is good, the quality of machining is good.

How much must IS rely on its own weapons production? How important is it when you look at the overall logistic requirements of sustaining a war?

If you look at the way they use weapons, they use improvised weapons in quite a conventional way, in the sense that most of their commanders are former Iraqi military officers or intelligence officers. So they tend to operate it to a large extent like a conventional military force. And they produce weapons to supplement their firepower and use them for specific operations.

When you look at what was discovered by your team: how sophisticated was the production?

These are improvised weapons in the sense that they use non-standard [material] that's not factory made or commercial-grade explosives or propellants. But the structure of production, although the workshops may look rudimentary, they were able to produce what they need, they produce them in high numbers and they produce them to a reasonably high standard, giving non-standard components. To compare them with another non-state or insurgent force, this is way beyond what we have seen before.

Your report states that chemical precursors for rocket propellants were procured in bulk via a robust supply chain, mainly from Turkey. How can IS operate a supply network for buying large quantities of those precursors over long periods of time without alerting intelligence agencies?

I think the Turkish government is very well aware that they are having a problem. They are taking steps to introduce some changes in their domestic commercial market regarding sale of things like potassium nitrate, which is an agricultural fertilizer, but it can also be used for the construction of homemade explosives. They are aware of the problem. But that does not negate the fact, that "Islamic State" has been able to tap into the commercial market in southern Turkey. For a long time, the border was more or less open between "Islamic State"-controlled northern Syria and southern Turkey - which is an interesting contrast between the "Islamic State" border with Turkey and the... Syrian-Kurdish border. And the latter is very much hermetically sealed. There is a lot of movement of commerce across the border. And we can see clearly from examining the supply chains of these component parts and chemical precursors that the group has been able to into the Turkish domestic market in bulk consistently over time. 

How difficult is it for CAR to get experts close to the frontlines like now in Mosul?

It is not difficult at all. We have had operations there for nearly two years, and we work as we work elsewhere in the world. That is: we embed with national defense and security forces. Whenever they overrun an enemy position, we were going after them and documenting weapons and ammunitions and related material on the ground. It is a logistically complex operation, but we are working with long established partners.

Is there a pattern that emerges about the chain of supply?

Initially - and this was quite widely publicized - there were large scale captures from the Iraqi defense and security forces. And we still find weapons in the hands of "Islamic State" which have been in Iraqi army stockpiles. They captured a lot of weapons and ammunition on the battlefield from the Syrian government forces. And more recently and increasingly, they are deploying weapons and ammunition which have come through northern Syria, so they have been supplied to rebel forces operating in northern Syria, primarily through Turkey, with international finance. Many of them have been manufactured in Eastern Europe. They have been shipped through to Turkey, supplied across the border to rebel forces in northern Syria and then "Islamic State" has taken control of them and moved them to Iraq.

How do your findings translate into speculation of how the offensive against IS in Mosul is moving forward: A lack of ammunition is probably not to be expected, since IS is producing its own weaponry. 

I won't speculate on how IS would be able to counter the offensive that is currently being waged against it. We cannot speculate. But what we can see in terms of their current supplies, they are using a lot of ammunition that is very recently manufactured - 2013, 2014, 2015. They have got quite heavy ammunition expenditures, but they are still supplied with weapons and ammunition which are coming into the conflict. So: For the most part, I would say that they have a reasonably healthy supply of weapons and ammunition.

James Beavan is Executive Director of Conflict Armament Research (CAR), a London-based NGO that focuses on "Islamic State" weapons procurement and manufacturing.