In military lexicon they are called ratlines. Right now around the besieged Iraqi city of Mosul, the term applies to the escape routes jihadists of the Islamic State (IS) group might use to flee, as the Iraqi Army continues its advance into the country’s second largest city.

A little over a week ago while on the frontlines around Mosul, I encountered a convoy of Iraqi policemen most of them Shia, on the dusty Nineveh Plain en-route to reinforce Iraqi Army positions east of the city.

Most of the men in the unit had seen recent action in the West of the country towards Tal Afar, a town near Iraq’s border with Syria.

Sitting as it does on the main road between Mosul and the Syrian city of Raqqa, Tal Afar has in the past been used by IS as a supply and logistical corridor and offers up the most obvious ratline out of Mosul.

For the moment, the job of cutting off Tal Afar as a potential IS escape route has fallen to the controversial Iraqi Shia militias operating as part of the Popular Mobilisation Forces (PMF). The unit of policemen I met that day appear to have been part of that operation.

In the main the deployment of the PMF remains something of a thorny issue in the Mosul campaign, given allegations of atrocities carried out by them during similar operations to free other Iraqi towns like Fallujah from the grip of IS.

“I’ve been fighting for one year now in many places, Ramadi, Fallujah, now Mosul,” one young masked policemen called Abdullah, from the unit told me, adding that Mosul was his home city and his family were still there under the rule of IS.

“Inshallah – God willing – I will see them all soon,” he added, before the convoy continued its journey towards the eastern flank of Mosul, where the Iraqi Army has now pushed its way into the suburbs.

Abdullah’s hopes of seeing his family however might yet be some way off if the resistance displayed by IS continues to intensify in its effort to hold on to the city.

Right now three questions have become the most pressing in terms of the campaign to liberate Mosul. The first is just what can the advancing Iraqi troops expect to encounter in terms of IS resistance once into the heart of the city? The second is what might become of IS should they be routed, and finally what will be the most challenging problems following Mosul’s liberation?

Some of the latest satellite images of Mosul produced by the independent geopolitical intelligence company Stratfor, have revealed how IS fighters have dug in and built a string of barricades on roads leading into the city in readiness for the final stages of the assault by Iraqi-led forces on the jihadist stronghold.

According to Stratfor, barricades built across key routes into the city have been made out of concrete blocks and other rubble, possibly from the concrete walls of destroyed buildings.

Roads still open in other locations have been lined with a stockpile of material, which could “easily be tipped” as anti-IS forces approach.

The photographs taken over the last few days also show that IS has cleared a wide swath of terrain to the north of Mosul airport, along the western bank of the Tigris River.

Nearly all of the buildings in the airport complex and the former military base to its west have been levelled.

By destroying the buildings, the jihadists are likely trying to transform the edge of Mosul’s fortified city centre into a wall from which they can target approaching Iraqi forces.

The large open areas IS has cleared to the south of its positions will enable it to watch and engage advancing forces from a greater distance.

In all there are estimated to be some 3,000 – 5,000 IS fighters in the city which is almost the size of Glasgow, alongside more than a million trapped civilians.

Some Mosul residents reached by phone describe other measures the jihadists have taken in preparation for the final stage of the assault by Iraqi Forces.

“I saw some Daesh (IS) members and they looked completely different from the last time I saw them,” said a resident of eastern Mosul who for safety reasons only gave his name as Abu Saif.

“They had trimmed their beards and changed their clothes,” the former trader said. “They must be scared ... they are also probably preparing to escape the city.”

Residents and military officials have told journalists that many IS fighters have already relocated from eastern Mosul to their traditional bastions on the western bank of the Tigris river, closer to escape routes such as the road through Tal Afar to Syria.

But other Mosul residents as well as military and intelligence analysts warn that IS will most likely put up ever more fierce resistance using whatever means at their disposal. They point to the fact that the city could potentially be turned into a kind of Arab Stalingrad, the city that suffered such devastation as Russia and Germany struggled for supremacy during the Second World War.

For Iraqi troops advancing into the urban labyrinth of Mosul it will be a terrifying experience. Reports suggest bridges that connect the two areas of Mosul on either side of the River Tigris have been mined and on the west bank of the Tigris, the maze of narrow alleyways there will force the Iraqis to abandon their heavy armour and fight on foot.

“The idea is just to create a huge improvised minefield, and when the enemy’s forces are trying to pick their way around them, they will open up with machine-guns or mortars. It doesn’t take many fighters to do that,” says Dr Michael Knights, of the Washington Institute For Near East Policy, who has spent time with Iraqi security forces.

IS have other weapons too at their disposal. As I saw time and again while with the advance on the towns and villages east of Mosul, a warren of tunnels has been constructed at almost every IS defensive position. Inside Mosul itself the jihadists having had two years with all the earthmoving equipment and labour at their disposal have created a vast subterranean network beneath the city.

Then of course there is the constant threat of chemical weapons use. While near the Makhmour front south of Mosul, I listened to accounts of how IS had used chlorine gas against Kurdish Peshmerga fighters there. I saw too the destruction caused after the jihadists set alight oil terminals and a sulphur dioxide plant that has left the sky south of Mosul full of choking black smoke and fumes for months now.

Above all else, concern over fighting inside the city focuses on those civilians who will be used as human shields to slow the offensive.

Some reports indicate that IS has forced women and children on to the tops of taller buildings to discourage airstrikes.

While the jihadists are working hard to keep Iraqi forces out, they have clearly exerted a lot of energy and time aimed at keeping Mosul’s innocent civilians in.

Crucial to minimising civilian casualties will be solid intelligence about the location of IS positions inside the city but this is easier said than done.

To encourage informants, troops have erected a number of mobile phone masts near the frontline and phone operators have given residents 60 minutes of free credit.

“It’s still dangerous to make calls,” said Mahmoud, a Mosul resident who would not give his real name.

“They’re searching people for SIM cards because they’re worried about spies.”

Should all these defensive preparations fail however and IS are routed from the city, what shape and form will the jihadist entity then take?

While the loss of Mosul in Iraq and possibly Raqaa in Syria would effectively destroy IS’s territorial “caliphate,” it would not eradicate it as an organisation. Most likely it would lay the foundation for the group to return to its roots as a more traditional insurgency, inciting violence in urban areas and seeking sanctuary in remote desert regions as well.

Terrorism analysts say that what comes next after IS depends on how you define the organisation in the first place and which of its three operational sections you are considering.

In the case of the IS core it stands to lose the most in terms of recruits, materiel, resources and supply lines from the capture of Mosul and Raqaa. There has been much talk about the danger of an exodus of foreign fighters from Iraq, but many intelligence analysts suggest those fighters will have a hard time returning home.

As for IS’s franchises and affiliated groups most have command-and-control networks that do not rely on the IS core. This most likely would lead them to develop their own ideological strains of jihadism shaped by local conditions and beliefs, which brings us to the final category of IS fighters, the grassroots supporters.

Among some grassroots jihadists there will likely be a degree of disillusionment over the fall of the “caliphate” and IS’s inability to fulfill its apocalyptic promises. But as many Kurdish and Iraqi officials told me, most will probably remain radicalised despite the core’s setbacks and already there are signs of new groups emerging to take over the IS mantle.

IS’s defeat in Mosul would also open the door to other jihadi groups seeking to exploit its disadvantage. Core al-Qaeda and the Syria Conquest Front-the al-Qaeda Syrian affiliate formerly known as Nusra Front-are likely to see IS’s weakness as an opportunity to ensconce their own position, particularly in Syria.

Which bring us to the third and final question concerning what will be the most challenging problems following Mosul’s liberation?

From the outset the battle for Mosul has involved a delicate military and political choreography.

Talk of “winning” in Mosul is highly relative. Yes, it is important to free the city from IS. Just as critical however is whether Iraq’s deeply divided factions can find a sense of unity, solidarity and political cooperation once IS in Mosul is dealt with.

Should they succeed in doing so positively, that political and civil outcome in Mosul will set a precedent for helping to deal with the human tragedy in Syria.

The alternative however could so easily tip Iraq into an all-out civil war, pitching Sunni against Shiite, Arab against Kurd, and Turkey, Iran, outside Arab states, and Russia and the West all competing to serve their own ends.

Just before leaving Iraq I put the question of what might unfold post Mosul’s liberation to both an Iraqi Army officer and a Kurdish politician.

“I’m a soldier and all that concerns me is defeating IS and I’m happy to have the Kurdish Peshmerga alongside us as allies, but the politicians are another thing,” was the officer’s telling reply.

As head of the Kurdistan Democratic Party’s (KDP) Foreign Relations Office, Hemen Hawrami is the consummate politician and diplomat, so I put it to him as to how confident he was on a sliding scale of one to 10 that the political situation following Mosul would be stable and positive?

“It’s a five” he replied. “It’s 50-50.”

Right now these tricky political issues might seem a long way off, but as the military noose tightens around IS in Mosul they will be sure to raise there head sometime soon.