By Sophy Ridge, Political Correspondent
It has begun. Eleven years after the invasion that marked the beginning of the Iraq War, Britain is again involved in a conflict in the region.
The Government is (rightly) quick to point out why this time, it is different.
The Iraqi government has made a formal request for British help in defending itself against IS and the US-led coalition is broad based, with support from some countries in the Middle East.

Most significantly, British involvement is limited to airstrikes and ground troops have been explicitly ruled out.
The first British jets took off for northern Iraq on Saturday morning. Precise details of their mission is not known.
There are just six Tornado GR4 fighter bombers stationed in Cyprus. To put this in context, Denmark is deploying more war planes than Britain.
Denmark has more war planes than Britain in the current conflict Ken Clarke has previously described the UK involvement as merely "symbolic", and others have argued that if it is so limited, what is the point of getting dragged into a potentially prolonged and complex conflict at all?
At the moment, UK military action is a halfway house.
Britain is not ignoring the crisis over IS and allowing other countries to get on with the campaign alone.
However, the involvement is incredibly limited.
Syria - where IS has its strongholds - is currently off limits. Ground troops are ruled out. MPs may have voted overwhelmingly in favour of airstrikes in Iraq, but many are extremely nervous about committing further.
The halfway house solution may work for the time being, but at some point the Government will have to decide whether the UK is fully in, or if it is out.
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Iraq's deputy prime minister Saleh al Mutlaq speaks to Sky News
A RAF Tornado GR4
A member of the aircrew prepares to depart on the first mission. Pic: MOD
The Tornados are being supported by a Voyager refuelling aircraft 
An RAF pilot at the base on Saturday morning
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The plane was carrying 248 people. Pic: @AndrewWork
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Sheikh Omar Bakri Mohammad
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