HMS Astute sailing to Faslane Naval Base in Scotland Flickr/UK Ministry of Defence If Scotland votes “Yes” on independence, it will begin a long process of creating its own naval defence force, a process that could leave its coastline at risk. The Royal United Services Institute, a British military think tank, said last week that Scottish independence would trigger a national debate over the U.K.’s nuclear weapons if the submarines carrying the Trident missile system were relocated to the south coast of Britain, away from the fleet’s current base in Scotland. The relocation could add £3.5 billion to the cost of maintaining the U.K.’s armed forces.

But there are larger concerns over the future of Scotland’s naval defenses. While Scottish independence would indeed spark a debate on Britain’s nuclear future, as well as kickstarting a costly process to relocate the submarine fleet, some experts caution that Scottish independence could leave it vulnerable to naval threats.

Put simply, the Russians sail their submarines into Scottish waters on a regular basis. Russian vessels approach Scottish waters about once or twice a year, close enough to require the Royal Navy to perform counter-maneuvers.

And Russia has a recent history of military adventurism, in the Ukraine. Although there is absolutely no reason for Russia to invade Scotland, the departure of Trident from Northern waters could — in theory — let the Russians do whatever they like up there.

The entire British nuclear fleet is based in Scotland

Scotland is currently guarded by a fleet of British warships and submarines. Five British submarines are based at Faslane Naval Base on the River Clyde in Scotland. Along with Britain’s Trident fleet, Scotland is also protected by three armed patrol ships and seven armed mine-hunter ships. As the UK Defence Journal reports, five more submarines are set to move to the Scottish base within the next few years. The U.K. Trident Programme is the controversial system of four nuclear submarines that are capable of launching the Trident II D-5 nuclear missiles. Since the submarines began patrolling the U.K coastline in 1994, they’ve been based at HMNB Clyde, part of the Faslane Naval Base.

Trident nuclear submarine HMS Victorious Flickr/UK Ministry of Defence

But despite the fleet of nuclear submarines and surface vessels currently stationed around Scotland, defence experts say Scotland’s naval defences are actually rather weak. Dr John MacDonald, director of the Scottish Global Forum, says that Scotland’s navy is already suffering from a “profound and fundamental” weakness. As Scottish First Minister Alex Salmond claimed in a 2013 speech, “the navy does not have a single major surface vessel based in Scotland.” Another weakness of Scotland’s current navy is the lack of maritime patrol planes. In 2011, the British government decommissioned the last of its Nimrod fleet. For over 40 years, Hawker Siddeley Nimrod planes provided maritime reconnaissance as part of Operation Tapestry, the patrol of the U.K.’s coastland. After the decommissioning of the last active Nimrod in 2011, Scotland’s coast was left with no maritime patrol planes, and the planned upgrades to the fleet have been repeatedly delayed.

If Scotland goes independent, Trident will leave

A Nimrod plane taking off in 2009 Flickr/Airwolfhound If Scotland votes for independence, a process will begin that will see the country gradually transition to hosting its own naval force. The current plan is to build a force of 2,400 regular personnel working across two squadrons. An independent Scotland would almost certainly force the British government to remove Trident from the Faslane base, leaving the country without any nuclear-powered submarines. Removing the Trident force from Scotland is certainly possible, although it will be costly.

A study published by the Royal United Services Institute estimates the price of the move to be between £2.5 billion and £3.5 billion. That’s cheaper than some predictions had previously estimated, with one figure of £20 billion now seeming unreasonably high.

Two countries are being heralded as the blueprint for Scotland’s naval ambitions: Denmark and Norway. Scottish Global Forum director Dr MacDonald stated that the Royal Danish Navy is “providing the inspiration” for Scotland’s defence ambitions. Presently, the Royal Danish Navy has over 80 vessels, with the Royal Norwegian Navy comprising of a similar number of ships. HDMS Thetis of the Royal Danish Navy Flickr/Boegh

While it’s established that Scotland is already lacking in naval defence forces, should we be worried about leaving Scotland without its full complement of submarines to patrol the icy waters around the River Clyde?

Many British government figures have expressed doubts over the plans laid out by Scotland’s government for the formation of a new naval defence force. A paper published by defence secretary Philip Hammond in 2013 claimed that Scotland will face an “immediate and pressing challenge” to establish its armed forces due to the small size of the £2.5 billion annual defence budget. As Scotland rushes to procure naval vessels, a newly independent Scotland could find itself facing a threat from overseas.

The Russians are always testing Scottish defenses

Almost every year, there are incidents around the Scottish coast involving the Russian Navy:

In 2010, a submarine that forms part of Britain’s Trident fleet was tracked by a specially upgraded Russian submarine as the English vessel attempted to leave the Faslane naval base in Scotland.

was tracked by a specially upgraded Russian submarine It was also reported in 2010 that British submarines were reporting the highest levels of contact with their Russian counterparts since the peak of the Cold War in 1987.

2011 saw a Russian aircraft carrier caught dumping waste off Scotland’s coast after being tailed by the Royal Navy destroyer HMS York. At the time, the Scottish National Party’s defence spokesman Angus Robertson accused the Russian navy of “fly tipping” and “bad manners.”

Russian aircraft carrier caught dumping waste off Scotland’s coast Russian warships are continuing to encroach upon Scotland’s coast on a regular basis. The most recent incident occurred days before Christmas in 2013, when a Royal Navy vessel was dispatched from the south coast of England after a “Russian task group” sailed near to the Scottish coast while on a training exercise in the North Sea. The Ministry of Defence did not disclose whether the Russian vessels sailed close enough to the Scottish coast to have entered territorial waters.

While the above incidents may not sound alarming, every one of them involved a Royal Navy ship. As Scotland scrambles to either purchase or build its own ships in the model of the Danish Navy, could there be a rise in the number of times Russia decides to test the U.K.’s coastal defences? Some may expect a rise in occurrences during the difficult change-over period, but it’s possible that Russia might even lose interest. It’s currently estimated that Scotland could be rid of the nuclear submarines by 2020. If Faslane is emptied of its stock of thermonuclear warheads and nuclear submarines, will there be anything left for the Russian Navy to snoop around?

We don’t know for sure what Russia is actually doing in the seas around Scotland (if anything). If Scotland votes to become an independent country on Sept. 18, Britain will become the first country in the world to host its nuclear arsenal in an independent country, and Scotland faces a daunting six years of change in its armed forces.