As the Iraqi army continues its operations in Mosul, ISIL's last stronghold in Iraq, the scale of the extremist group's capabilities is becoming clearer. CCTV’s Jack Barton was given an exclusive tour of what appears to be one of ISIL’s largest bomb factories.

Clearing houses on the edge of Mosul men from an Iraqi artillery division discovered a few homemade ISIL rockets and mortars, nothing too unusual.

"There are almost eleven ISIL shells… standing up. This is like a prototype for the final product that was made at this factory," Muhsen Uqla, artillery instructor of Iraqi Army, said.

Factory is the right word for what the soldiers then discovered inside. Every single room in this large warehouse yard is a different step on an assembly line geared to mass-produce mortars that I’m told that have a range of six kilometers.

This is the scrap metal ISIL were making their bombs out of. They would gather it up here and then we can see some examples over here of when they had actually made the bomb in the mold.

Room after room, from tail fin assembly to the paint shop…. A box of fuses to be screwed into the tips of the bombs.

Often when we think of a terrorist bomb making operation we think of a basement or a room hidden away somewhere, but this is genuinely a factory. It is terrorism on an industrial scale.

The men who found it say they’ve never seen anything like it.

"We’ve been in a lot of battles and we saw a lot of bomb factories in Fallujah, but this one is the biggest we have seen so far," Uqla said.

Mortars along with snipers and suicide vehicles are a key component of ISIL’s defense arsenal in Mosul.

"You see all those shells. They were supposed to be used against us. Thank god we captured it," Uqla said.

One arms factory neutralized. But the soldiers here have no doubt there are more ahead.