Road to Mosul: 'The Humvee we parked beside disappeared in a mushroom cloud'

I felt the blast from an enormous explosion and spun round.

The Humvee we had been parked behind a few minutes before disappeared in a mushroom cloud of smoke and debris; it was gone.

Four Iraqi soldiers had died. Victims of yet another vehicle suicide bomb attack on the convoy we joined in the early hours of the morning.

This is the Iraqi army's elite Golden Division's first foray into the battle to relieve Mosul from the grasp of Islamic State. It is going to be long and bloody.

From early morning huge numbers of troops, Humvees, tanks, weapons systems and mine clearance vehicles edged their way down to the town of Bartella on the road to Mosul.

The Mosul Brigade we were with was tasked with clearing the main road to the centre of town.

The whole area had been pounded from the sky. Not a building for mile after mile was untouched; debris was strewn across the highway and we dodged bomb craters every few meters.

We found ourselves right at the front, near a tank providing protection for mine clearance engineers identifying IEDs.

They are doing this job under constant fire. This is urban warfare, it was always going to be like this.

There are pockets of Islamic State everywhere. As soldiers identify targets they open up.

Despite their firepower the incoming rounds are constant.

Dodging to take cover, we came under attack from two sides; high calibre rounds whizzing past us. The Iraqis returned fire to the left and right.

It was almost impossible to keep our bearings as we dodged between Humvees, jumping into our seats, bolting down the hatches.

We knew the convoy would be a target for suicide bombers in cars and they struck a hundred metres or so in front of us but failed to get past the tank that destroyed the vehicle.

As the battle intensified, helicopter gunships were brought forward to unleash their enormous firepower on the Islamic State positions.

Rockets smashed into buildings. Moments later, the sound of huge explosions reached us.

On the right and left flanks, attempting to enter the town from the desert, two brigades joined the assault. From the distance we could see they too were under fire.

Islamic State is spread across the front of the town.

It is likely there are not many of them and that, to a degree, is the point; determined and as prepared to die as they are, Islamic State can inflict terrible damage and bring the progress of an assaulting army to a near standstill.

Bartella is just the first reasonably sized obstacle the Golden Division has come up against. While the progress has been slow, it has been effective.

A senior commander told me that he expected the start to take time but that once they were through the outer edges of the town he was certain they would move quickly.

The push for Mosul is now fully on. Despite optimistic noises this campaign is going to be hard and will cost many lives. The scorched earth tactic of Islamic State takes no prisoners.