US strategy against IS

What has the US's strategy against IS, with Operation Inherent Resolve, achieved so far?

It certainly contributed to halting ISIS in its tracks and from reaching Baghdad or Erbil in the north [of Iraq], both of which would have had serious political effects. And it meant that there is now a fairly stable front line in Iraq, stretching from Kurdistan to Anbar province.

Quite clearly, the air campaign has limited ISIS's capabilities. I suspect that one of the reasons that their propaganda video operation is less prolific than it used to be is because of security precautions, and they haven't been able to stage a grand offensive, a big attack out of this front line. There's been fighting going backwards and forwards, but the front line is pretty stable.

In addition, the coalition air strikes prevented the fall of Kobani and has now allowed a certain amount of pushing out from Kobani by Syrian Kurdish fighters and some allied groups.

The US is also involved in training and advising Iraqi and Peshmerga brigades so that they can launch their own offensive against IS, presumably that will take time?

[Iraqi] Prime Minister Haider al-Abadi said at the Munich Security Conference that the offensive would start in the summer - I think that's going to be a big ask, there'll be difficulty for the Iraqi authorities taking forces from the front line for re-training, they'll be extremely cautious about that.

In addition, the Iraqi forces were severely damaged over the last few years, not just by ISIS destroying the equivalent of four divisions worth of strength, but because of the politicization of the armed forces, whereby capable military commanders were replaced with political cronies of [former] Prime Minister Maliki and his crew. And the toleration of egregious corruption has severely weakened them.

I know the US will do everything they can to build on the competent, combat-proven commanders, and Abadi has sacked a lot of senior officers, but I'm afraid I'm not optimistic about the speed at which that capability can be introduced.

What does the hybrid nature - a mixture of insurgency, terrorism and infantry - of IS mean for US military strategy?

What we saw last year is that ISIS was acting as a guerrilla force, a highly mobile force of light infantry and technicals, but it is also an insurgency cooperating with other Sunni insurgent groups.

So, although there is a pretty stable front line between ISIS-controlled and Kurdish and Baghdad-controlled territory, ISIS is still present in some strengths in Sunni areas and that's where the car bomb and suicide attacks that are killing people daily are coming from.

The other problem with ISIS is that compared with other groups, it doesn't at all appear willing to negotiate, it's been described as a death cult, it's extremely nihilistic.

Do you think the US's response to ISIS and its special type of warfare has been appropriate?

First of all, there's nothing new about hybrid conflict - one example is the American War of Independence. The solution to it is not just capable military forces, it's a comprehensive approach, it's diplomacy, intelligence, economic support and development.

And, particularly in the 21st century, it's about countering a sophisticated propaganda and information operation. That's the most difficult part of it - and that applies to Ukraine, Iraq and Syria.

US President Barack Obama has said he will not deploy ground troops in the fight against IS. Is he right?

It's quite clear that the Baghdad government doesn't want US combat forces on the ground, nor do the Shia militias supported by Iran. After what's happened in Iraq in the last decade, it's unrealistic to expect them to welcome combat units on the ground.

Ben Barry is senior fellow for land warfare at the London-based International Institute of Strategic Studies (IISS). He served as an infantry officer in the British army, commanded a NATO brigade in Bosnia and held various positions in the UK's Ministry of Defence (MOD). He also led the British army's analysis of the lessons of the Iraq campaign.