Among other things, an independent Scotland would require the UK government to find a new home for its Trident nuclear weapons system. It's an issue that has received surprisingly little attention this week, with most commentators focusing on the economic implications of independence, but it is one of the thorniest. Almost all of the UK's nuclear submarines are stationed at the Faslane naval base on the Clyde, while the warheads and missiles are stored at Coulpor on Loch Long, but the unilateralist SNP has long pledged to remove them from Scottish waters if it wins control over defence policy (currently a reserved matter for Westminster).
Initial work has already begun on the replacement of Trident (although the final decision won't be taken until 2017) but finding a new site for the submarines and warheads would dramatically complicate the process. As Professor William Walker wrote in the Scotland on Sunday:
Although a harbour might be adapted to function like Faslane, establishing another Coulport - at a location that would meet stringent safety and logistic requirements - would be extremely difficult. Furthermore, transfer south would require huge investments to replace infrastructure built in Scotland over decades.
The only viable alternative base to Faslane is Devonport in Plymouth, where three Trafalgar-class nuclear submarines are currently stationed (they are in the process of being moved to Faslane). But this still leaves the government without a new site for its missiles and warheads.
In practice, the UK government would likely attempt to persuade Scotland to retain Trident in exchange for concessions on other issues such as the national debt, sterling and North Sea Oil. But with a significant body of political and military opinion now convinced that the costs of Trident outweigh the benefits, the case for UK nuclear disarmament would be all the stronger were Scotland to go it alone.