ON SEPTEMBER 17th the newly formed National Security Council (NSC), chaired by the prime minister, David Cameron, will begin discussing how to cut Britain's defence budget. The conversation will be informed by the Strategic Defence and Security Review, which the coalition government embarked upon within weeks of taking office. Whereas the last such exercise, completed by the Labour government in 1998, took over a year to conclude, this one must be finished by October 20th, when the coalition will announce the results of its overall review of public spending. The outcome of these deliberations will define not just the shape of Britain's armed forces, but also its role in the world and sense of itself as a nation.

It is not just the rush that is making this such a difficult and painful process. Britain's annual defence budget is around £40 billion ($62 billion), including the extra cash (£4.6 billion this year) that the Treasury provides for operations in Iraq and Afghanistan. That is munificent by international standards—Britain ranks third in global defence spending, behind America and China. But defence benefited much less than other departments from the largesse of the boom years (see chart). The Labour government was ignobly reluctant to meet the costs of its lengthy military engagements.

It also abjectly failed to reform the wasteful procurement regime at the Ministry of Defence (MoD). As Liam Fox, the Conservative defence secretary, has argued, even by Labour's profligate standards, the financial situation he inherited is unique. In a speech last month, Dr Fox identified “an unfunded liability in defence of around £37 billion over the next ten years.” Under Labour, the MoD ordered equipment costing over £20 billion, “without ever having an idea whether the budget would be able to afford it”.

All that created a chasm between Britain's military ambitions and its capacity (or willingness) to pay for them. Now an overstretched defence budget faces a massive cut: as part of the bid to address Britain's fiscal deficit, defence faces a cumulative squeeze of between 10% and 20% over five years. The result is some very hard and worryingly hurried choices. Since Britain is America's most important military ally, they will be keenly awaited in the Pentagon, as well as Whitehall.

Were Britain prepared to sacrifice some of its global influence and prestige, those choices would be easier. Some argue that the real threats to Britain's security—invasion or attack by a powerful state—have rarely been smaller, and that defence spending should decline accordingly. Many, including quite a few Liberal Democrats, the Tories' coalition partners, would like Britain to get out of the business of projecting large-scale military force overseas. Instead, they argue, Britain should humbly focus on meeting the collective security obligations imposed by NATO membership, limiting its expeditionary goals to humanitarian interventions approved by the United Nations, rather like Canada and some of the Scandinavian countries.

There is not the slightest sign, however, that the government intends to reappraise Britain's traditional ability to “punch above its weight” militarily and diplomatically. In another recent speech Dr Fox said that the country needed “robust and well-equipped armed forces, capable of intervening abroad whenever necessary.” But whether Dr Fox, a right-winger with neoconservative leanings, can reconcile that aim with the demands of an impatient Treasury is questionable. His strained relationships with the three most powerful members of the NSC—Mr Cameron, George Osborne, the chancellor of the exchequer, and William Hague, the foreign secretary—may also affect the wrangling.

Fighting the next war

Dr Fox and the NSC must begin by balancing Britain's current obligations in Afghanistan with the challenges of the future. According to Malcolm Chalmers of RUSI, a think-tank, even though continuing operations in Afghanistan are notionally funded by the Treasury, the campaign is still absorbing about 30% of the MoD's budget. That is because sustaining roughly 10,000 troops in Afghanistan ties up many times that number in training and support. That means the army will perforce be largely protected from the immediate savings the government is looking for—increasing pressure on the other services.

Yet the fact that Britain has recently been involved in two troop-heavy counter-insurgency campaigns does not mean that all or even most future conflicts will be similar. In ten or 20 years the threat from jihadi terrorists operating from failed states may have receded. Iran could trigger a nuclear-arms race in the Middle East. Violent competition over scarce resources may erupt with or between emerging superpowers, such as China and India. And so on into the unknown unknowns.

One obvious approach would be to inflict equal pain on each of the services. But Dr Fox has described that method as “intellectually indefensible and strategically dangerous”. He also rejects the idea of simply trying to do what Britain does now, but with less money, since that would mean neglecting investment in new fields such as cyber-warfare. Dr Fox is sounding radical—perhaps too radical, given the uncertainty about future threats.

Up to 40 separate studies of defence expenditure are close to completion, which will be submitted to the NSC's small secretariat, led by the new national security adviser, Sir Peter Ricketts, a former head of the Foreign Office. The indications are that the individual services are reluctant to compromise. The army is arguing that big reductions in its size would lead to a collapse in morale, particularly among officers who would see their career prospects diminished. The navy insists that it is already at or near the minimum needed to be a coherent maritime force (it already has less than a tenth of the number of ships it boasted in 1945). As for the Royal Air Force (RAF), it stubbornly clings to a view of itself as a miniature version of the American Air Force.

One of the gravest problems is the way a number of very large procurement programmes are bunched together over the next few years. They include the purchase of 40 more Typhoon aeroplanes for the RAF for around £2.8 billion; two new 65,000-tonne aircraft carriers that are due to come into service in 2016 and 2018, at a cost of £5.2 billion; the 138 F-35 strike fighters that go with the carriers (about £10 billion); seven Astute-class attack submarines, the first three of which cost £4 billion; and the £20 billion programme to replace the Trident nuclear deterrent.

The RAF looks certain to be hit hard. Douglas Barrie, of the International Institute for Strategic Studies, reckons that the air force will shrink dramatically, losing perhaps 200 jets through the early retirement of Tornadoes and Harriers and a scaling back of the plan for a 160-strong Typhoon fleet. Attack helicopters and unmanned drones will increasingly be used to support ground operations instead. The order for F-35 jets, which are to be shared between the navy and the air force, looks certain to be more than halved to around 60, saving more than £5 billion in purchase costs and at least as much in maintenance.

Theoretically, one or both of the navy's aircraft carriers could be cancelled. That would drastically reduce Britain's expeditionary capability; but the advanced state of construction, the amount of money already spent and the 10,000 or so jobs at stake make it unlikely. Ditching just one of them is impractical, since two are needed if one is to be continuously available for operations. Despite some excitable recent talk of sharing a carrier with France, the difficulty of agreeing what to do with such a shared vessel make that idea unworkable. Dr Fox has ruled it out, though he is exploring other areas of co-operation.

The conspiracy of optimism

The most controversial programme of all is the replacement of Britain's Trident nuclear submarines (Dr Fox has wasted political capital in a fruitless row with the Treasury about who should pay for the renewal). The coalition is committed to keeping the deterrent, albeit with the reluctant support of the Lib Dems. But it may be possible to delay ordering the new boats by several years, and to make do with three submarines rather than the current four. That would put back the costs and save several billion pounds. Alternatives to Trident, such as converting an attack submarine to do the job, seem likely to be dismissed on grounds of cost and effectiveness.

And despite Afghanistan, the army will not escape entirely. A growing emphasis on special forces in ground warfare, combined with rising scepticism about the future utility of heavy armour should allow two or three battalions of infantry to be eliminated, the mothballing of most of the army's main battle tanks and thus big savings in manpower and logistical support. A smaller army—comprising perhaps 95,000 soldiers rather than the current 107,000—would also make it possible to repatriate most of the roughly 19,000 British troops still stationed in Germany without building new bases or housing.

Less sexy than those headline cuts, but just as important, are the savings to be made in the way the MoD itself operates. Above all, it needs a rational procurement policy. An independent report it commissioned last year described a “conspiracy of optimism” between the services, the defence establishment and industry. Knowing that major programmes are rarely cancelled outright, each of the armed forces has a systematic incentive both to underestimate the likely cost of equipment and to aim for the highest possible specification regardless of risk. The results are routine delays and vast cost overruns.

So there is a pressing need to bring order and sanity to Britain's overstretched defence budget. But that cannot be achieved overnight. Given the ten-year time horizon that defence planning requires, attempting severe cuts too quickly may be risky militarily and financially, since it might prove costlier to revive needed capabilities in the future than to preserve them now. That will be the message that Dr Fox will take to his colleagues on the NSC. It may well fall on deaf ears. The government's priority is the deficit, not a sensible defence review.

The sun sets on Trident, but only literally