The SNP's sketchy plans for the defence of an independent Scotland are half-baked The referendum on independence for Scotland will take place in autumn 2014. Between now and then, every aspect of the relationship between an independent Scotland and the remainder of the UK - known unflatteringly as "rump UK" ("rUK") - will be debated in fine detail. Defence will figure prominently: the maintenance of effective armed forces is an attribute of independent statehood. But armed forces are also expensive. In October 2012 the Scottish National Party promised that "an independent Scottish government led by the SNP will commit to an annual defence budget of £2.5bn." What is the logic behind this budget and how much defence - and of what sorts - could it actually buy? The proposed budget is significantly less than the £3.3bn which Scotland currently contributes to overall UK annual defence spending of about £35bn. The SNP have explained that the figure of £2.5bn represents both "an annual increase of more than £500m on recent UK levels of defence spending in Scotland" and "nearly £1bn less than Scottish taxpayers currently contribute to UK defence spending." So the political/electoral logic is compelling enough: Scottish taxpayers are promised more defence for their money as well as more fairness. But closer inspection reveals the SNP's promise to be based on questionable assumptions. In the first place, UK defence spending benefits from economies of scale which would not necessarily be available to an independent Scotland. There are also decades of sunk costs within the UK defence budget which will not automatically transfer to Scotland. There are buildings, facilities, training areas and equipment owned and used by the Ministry of Defence in Scotland which might not be given away. And neither is it clear that adequate provision has been made for Scotland's share of accrued defence debt, through projects completed under the Private Finance Initiative, for example. What could Scotland's taxpayers get for their money? They are very unlikely to be in the market for large warships, modern combat aircraft and so on, because of the considerable costs associated with training and maintenance. And it is difficult, in any case, to see what contribution two or three frigates, or half a dozen combat aircraft could usefully make to the security of Scotland's land mass and its people's interests. What is more realistic is a fleet of inshore patrol boats and support vessels (probably built outside Scotland because its naval shipyards will have ceased to be viable), with tasks limited to customs inspections, counter-narcotics patrolling, visits to offshore oil and gas facilities, and maritime rescue. As for air power, Scotland's low-budget air force might comprise a small fleet of helicopters, working in conjunction with the Scottish coastguard, as well as a few medium-sized transport aircraft which could be used for aid delivery or for charter to UN operations and the like. More ambitiously, Scotland's army would be organised into two Multi-Role Brigades; one at full strength and one reserve. If the strength of each of these brigades is about 5,000, and if they must cover all the usual functions of a ground force (fighting troops, communications, medical support, logistics and supply), while maintaining a viable reserve, then the deployable strength on an international peacekeeping operation might be little more than a battle group (or at the very most two) of about 700-900 combat-ready soldiers, to be replaced after some months by troops fresh from training. A force of this size might find it difficult to mount a non-combatant evacuation operation from a Scottish diplomatic mission in a conflict zone; another country or organisation would have to help in such dire circumstances. The SNP's position on security and defence policy is clearest where nuclear weapons are concerned. First Minister Alex Salmond has insisted that it is "inconceivable that an independent nation of 5,250,000 people would tolerate the continued presence of weapons of mass destruction on its soil." But this position is inconsistent with the SNP's new plan for Scotland to become a member of Nato. The SNP insists that an independent Scotland will take up membership of Nato provided the Alliance "takes all possible steps to bring about nuclear disarmament as required by the Nuclear Non-Proliferation Treaty." It is certainly the case that not all members of Nato are nuclear weapon powers; the lack of nuclear weapons is therefore no bar to membership. But Nato is, deliberately and knowingly, a nuclear alliance. Why then, would Nato governments accept a new member so openly and actively opposed to nuclear weapons? A more fundamental problem concerns the SNP's understanding of collective defence. The SNP insists that independent Scotland will remain in Nato provided the Alliance "continues to respect the right of members to only take part in UN sanctioned operations." This challenges the collective defence provision which is at the very core of Nato. According to Article 5 of Nato's founding treaty, members of the Alliance will consider an armed attack on any one of them to be an attack on them all. Each member then undertakes to assist the member being attacked and to take "such action as it deems necessary, individually and in concert with the other Parties, including the use of armed force." There is a sense of immediacy in this language, and even a degree of automaticity. There is, however, no sense that a Nato member should first seek UN approval being going to the aid of its allies. The SNP's outlook on security and defence policy is more of a sketch than a full strategic assessment. Such an assessment would show that Scotland has just three options. First, if an independent Scotland wishes to be a serious military actor then it will most likely only be able to do so in conjunction with either the forces or the finances of the rUK. If offered something very substantial in return (the basing of Trident nuclear submarines and missiles in Scotland, for example), then the rUK might perhaps cover the underlying costs of Scottish defence, enabling the development of militarily capable "pocket forces" by their neighbour. The second option would be for Scotland to make no more than a token effort at security and defence, offering some specialised capability for humanitarian operations for example. But with a security and defence budget as small as this, the real question is why bother at all? The third option would be for Scotland to satisfy itself with freeriding on others" efforts and expenditure, keep its limited funds in the bank and hope for the best. Three options: work with the UK; make a token effort; or don't bother. Paul Cornish is the Professor of Strategic Studies at the University of Exeter