How much force will, or can, the UK bring to bear against IS?

"Operation Shader", the British component of the air campaign against the so-called Islamic State (IS) organisation, is limited in both scope and resources even while its ultimate duration still remains far from clear.

From the outset there has been a lack of congruence in the strategic geography because of the different situations in Syria and Iraq.

IS has rolled out its new caliphate across a swathe of Syrian and Iraqi territory.

The US and many of its Arab allies are conducting air strikes against targets on Syrian soil.

This is after all where IS's centre of gravity resides.

And the fighting around the Syrian Kurdish town of Kobane - hard up against the Turkish border - has taken on a kind of emblematic significance.

But Britain has held back, the government perhaps smarting from the decision of the House of Commons, in August 2013, to refuse authority for punitive air strikes against the Syrian regime.

It thus determined to restrict its request for parliamentary approval for air strikes to Iraqi territory alone while leaving the issue of Syria open for the future.

Initially six fast Tornado jets were despatched to RAF Akrotiri in Cyprus, along with an air-to-air tanker, with two more Tornados being sent once offensive air operations began.

The initial UK deployment came when concerns were essentially humanitarian in nature with growing alarm at the fate of the Yazidis and other minorities in the face of advancing IS forces.

In the event no major British humanitarian operation was required though British troops and Chinook helicopters were ready if needed.

Military assistance is also another crucial element of the package.

Some 320 tonnes of weapons, ammunition and military equipment have been provided to local enemies of IS.

British troops have trained the Kurdish Peshmerga fighters in the use of heavy .50 caliber machine guns.

This though is only a taster of the training that might need to be provided in future if credible local ground forces are to be established.

An RAF Rivet Joint RC135W electronic surveillance aircraft was deployed to Qatar and in mid-October the available intelligence assets were expanded by the use of a small number of Reaper drones that have been re-located from Afghanistan and are being operated from the Gulf.

Once again a significant element of the RAF contribution relates to intelligence gathering, though the Reapers have the ability to complement the Tornado strike sorties if needed.

As if to highlight the common terrain in which IS is operating the Reapers and the Rivet Joint are allowed to gather intelligence inside Syria though RAF aircraft are not allowed to strike at Syrian targets.

On 30 September a pair of Royal Air Force Panavia Tornado GR4 aircraft engaged their first targets in Iraq.

Conducting an armed reconnaissance mission out of RAF Akrotiri they "were tasked to assist Kurdish troops in north-west Iraq who were under attack".

What the Ministry of Defence (MoD) describes as "a heavy weapons position" was located using the Rafael Litening III targeting pod and destroyed using a Raytheon Paveway IV precision-guided bomb.

Following this the patrol identified an armed pick-up truck in the same area and attacked it using an MBDA "Brimstone" missile.

Since then, according to Defence Secretary Michael Fallon, "the RAF has flown 37 combat missions, conducting 10 successful strikes, providing valuable intelligence and surveillance and helping to halt ISIL's (Islamic State's) advance."

While few operational details are available it is believed that pairs of aircraft are conducting flights almost daily.

Much has been made of the Tornado's particular capabilities in terms of both its capacity for gathering intelligence and its ability to deploy specialised precision-guided munitions.

Tornado may be an older air-frame but it remains a remarkable weapons system.

Raptor - the Reconnaissance Airborne Pod for Tornado - is a stand-off electro-optical and infrared long-range photography pod.

It can create hundreds of images during a single sortie.

The Litening III Laser targeting and reconnaissance pod provides a vital air-to-ground targeting capability.

This together with the use of sophisticated munitions like the laser-guided Paveway IV and the Dual-mode Brimstone enhances the aircraft's performance and reduces the likelihood of targeting errors.

Western contributions to the US-led coalition include:

Britain: Eight Tornados, a tanker and an electronic reconnaissance aircraft

France: Nine Rafale jets, an Atlantique 2 maritime patrol aircraft and a C135-FR tanker

Australia: Eight F/A-18F Super Hornet jets, a Wedgetail Airborne warning and control aircraft and a KC-30 tanker

Belgium: Six F-16 jets

The Netherlands: Eight F-16 warplanes

The RAF clearly has some intelligence gathering capabilities that other countries don't have and even its small contribution of Reaper drones will be welcome to the Americans for there are simply never enough unmanned aerial vehicles (UAVs) to provide sufficient coverage.

But this is an air campaign of largely penny packets.

Leaving aside the large US air forces already established in the Gulf and elsewhere in the region, together with Washington's Arab allies who are operating from their home bases, most countries are making only small contributions.

Some 10 strikes by the RAF in a month is hardly a high-intensity campaign but given that there seems little idea of how long this is all going to last, is it possible to give any sense of the long-term costs of the operation?

Malcolm Chalmers, research director at the Royal United Services Institute, told me that "the direct additional costs of the commitments made so far, stretched over a year or so, seem unlikely to exceed the costs of the Libya operation", which were about £250m.

But he warns: "They could get a lot higher if large ground forces got involved - which seems unlikely - or if more aircraft were brought in in order to bolster the commitment."

Mr Chalmers notes that "the RAF has been maintaining a high level of operations in Afghanistan in recent months, and this has limited its ability to transfer assets to Iraq.

With the recent withdrawal of combat assets from Afghanistan, this will give the government more choices as to whether to do more in Iraq.

Given expectations of a long and complex campaign, he says, "those involved will want to be confident that operations can be sustained for a long period, potentially for several years."

The government will also be wary of devoting too many assets to Iraq/Syria - other demands may emerge elsewhere.

Of course, the end of combat operations in Afghanistan was not supposed to usher in a new military campaign but to lead to a period of consolidation and re-organisation - a period that in all likelihood would be characterised by continued pressure on defence spending in the absence of a serious up-turn in the country's finances.

The air campaign against IS may be relatively small scale but it has already revealed some strains within the RAF.

The 40-year-old Tornado is the only aircraft in the RAF inventory with a precision ground-attack capability.

The RAF Tornado force - once 11 squadrons strong - is now made up of just three squadrons of about 16 aircraft each.

But in many ways it is busier than ever with operations in Cyprus, Afghanistan and its first operation in Africa.

The Iraq crisis has prompted the decision to delay disbanding a third Tornado squadron.

Efforts are being made to see if the integration of the Brimstone missile on the Typhoon can be accelerated and Typhoons capable of delivering Paveway IV's are slowly entering service.

Nonetheless the pressures are there for all to see.

And these pressures are not going to go away.

Next year's Strategic Defence and Security Review (SDSR) also casts a shadow over all this.

Given the government's commitment to further tax and spending cuts, it is hard to imagine that the MoD will escape further cuts in its own capabilities.

Indeed, Brig Ben Barry, land warfare analyst at the International Institute for Strategic Studies (IISS) in London, already detects signs of a certain drawing in of horns.

"The decision," he told me, "to have no more than a minimal presence in Afghanistan after 2015, the outcome of the September 2013 parliamentary vote which vetoed UK strikes on Syria, the accumulated political delays in authorising British forces to strike on Isis [IS] and the relatively small size of the RAF contribution to that operation, all signal strategic caution by the UK government."

This reflects public mood at the end of the war in Afghanistan.

"These factors have probably reduced UK military influence with the US and in the Gulf," he says. They have led to more strain.

The combination of reconnaissance operations against Boko Haram in West Africa, the Ebola mission and the counter-IS campaign means that the operational demand on some capabilities has been greater than anticipated.

This, says Brig Barry, has resulted in greater stress on the RAF's C17 fleet, its Tornado jets and small fleet of ISR (intelligence surveillance and reconnaissance) platforms and personnel.

The planned recuperation of some military capabilities after withdrawal from the combat role in Afghanistan has been disrupted.

But here is the fundamental point: As Brig Barry notes, even before the irruption of IS, the key strategic issue facing the UK was the deterioration in Europe's security position, which was not anticipated in the 2010 SDSR.

This includes the increased instability in Nigeria, the Sahel, the Maghreb, Egypt, Lebanon, Iraq and Syria, with domestic security authorities deeply concerned about the prospective return of UK citizens with jihadi experience.

If the UK is to honour its Nato Article V commitments in Eastern Europe by deploying credible forces, it will require the rebuilding of combat capabilities that have atrophied in the past decade.

These include maritime and air operations in contested battle space, as well as armoured warfare and countering heavy indirect fire capabilities.

There are rarely holidays from strategic concerns.

The threat picture has got much more complicated and the resources available that much more scarce.

That's why getting this campaign against IS right is going to matter.

But for now it has barely begun.

Air power is clearly no panacea. It has struggled to keep the Kurds in contention in Kobane.

Indeed to be fair to the Americans, the British and others they have never claimed that air power can stand in for local fighting forces on the ground.

The problem here is that there is not just an incongruence in terms of strategic geography - the conflicting local scenarios in Syria and Iraq.

There is also an incongruence in terms of time.

Military power is all about delivering overwhelming effects but without capable ground forces this cannot be done.

So air power is a stop-gap for the medium term and nobody yet seems to have any clear idea as to how long it will take to muster, select, vet and train "moderate" Syrian fighters let alone to restore some credibility to Iraq's shattered military.

We are dealing here with but one aspect of the crisis of the modern state in the Middle East.

The complexities are enormous and the debates are more about governance, democracy and stability than purely military factors.

Malcolm Chalmers of RUSI sees a fundamental problem when considering Syria. "It just doesn't make sense," he says, "for the US to say it wants to build up the more moderate anti-Assad rebels and then not be prepared to defend them against President Assad.

"In the absence of a more coherent US strategy for Syria, I think the UK would be well advised to keep to its current Iraq-only approach, where I think the case for military action is more urgent and more likely to help."