Sweden promises to use force over "Russian sub" as Baltic hide and seek goes on

Supreme commander says craft must be brought to surface while Swedish ships comb archipelago outside Stockholm

Sweden’s armed forces chief said on Tuesday that the military would attempt to force a suspected Russian submarine that has intruded into its waters to come to the surface.

Marking an escalation in rhetoric over the alleged incursion, Gen Sverker Goeranson said the Scandinavian country wanted to send “a very clear signal” that its armed forces were “acting and are ready to act when we think this kind of activity is violating our borders”.

“Our aim now is to force whatever it is up to the surface... with armed force, if necessary," the supreme commander added.

The general’s words marked a change of tone in what has previously been described as an “intelligence operation” to establish the source of “foreign underwater activity” detected in the Baltic, close to Stockholm.

His comments raised the spectre of an international stand-off if Sweden employs depth charges to goad the vessel up from below.

The unidentified vessel was spotted surfacing in the Stockholm archipelago twice on Friday and once on Sunday, and Gen Goeranson said on Tuesday there had been further observations in the last 24 hours. A force of up to 200 men with fast-attack boats, minesweepers and helicopters was combing Ingarö Bay and areas further south.

While the armed forces have refused to say they are hunting a submarine or to identify whom they believe is controlling the mysterious craft, military analysts believe it is most likely a Russian submarine or mini-submarine, a charge that Moscow denies.

On Tuesday, the Swedish navy’s HMS Visby, a stealth craft armed with Bofors guns, guided missiles and a powerful sonar was among those leading the hunt for the vessel.

The Telegraph was able to circle the Visby in the Hulk, a small hired boat, as the ungainly-looking corvette with its sculpted carbon-fibre shell - designed to confuse enemy radars - patrolled an area at the southern end of the Stockholm archipelago.

This giant sneeze of 30,000 rocky islands and islets spreading into the Baltic from the Swedish capital is know for its wild beauty. Ingmar Bergman set some of his early films here and the bathing nudes of Anders Zorn, Sweden’s most famous painter, drape themselves on its shores.

Many Stockholm families spend their summer holidays in cottages set on the islands, among the countless inlets and “wind-tormented” fir trees.

But the archipelago also has a less romantic history, tangled with its mighty neighbour across the Baltic. During the Great Northern War in the early 1700s, the Swedish Empire clashed here with Tsarist Russian forces who left burned towns and farmsteads in their wake. Almost three centuries later, the Soviets sent scores of submarines into Swedish coastal waters, many of them probing between these islands.

That “submarine crisis” – in which Sweden reported between 17 and 36 "foreign operations" every year in its territorial waters during the 1980s – seems not so distant to many locals.

“I was serving on a missile ship, the HMS Ystad, in 1990 when there was a submarine alert in the middle of the night,” remembered Fredrik Sandberg, aphotographer who was also pursuing the Visby on Tuesday. “We replaced the missiles with depth charges, and rushed to the scene but we could not detect the sub.” In a bizarre finale, the Swedish sailors did an exercise to simulate dropping the charges by rolling potatoes into the water at intervals.

On Tuesday morning, the tension of past years was back as the Visby stood out on the horizon off Muskö, an island about 30 miles south of Stockholm. Muskö was once home to a huge underground naval base, with dry docks for destroyers and submarines. Only some parts are still used by the military.

Experts say Sweden’s anti-submarine capability – which once include sophisticated helicopters - has been seriously depleted in recent years after the Cold War appeared to close that chapter.

“All the Visby can do is listen with its sonar but there is so much other traffic in these waters – like us - that a mini-sub could easily escape detection,” said Ulf Busch, 71, the skipper of the Hulk, as he manoeuvred around the corvette.

Back on land, in the small coastal town of Nynäshamn, locals were tucking into platefuls of raggmunk (potato pancakes) served with bacon and lingonberries at the Flötet café on the quay.

“I think this submarine story all has to do with Ukraine and [Russian president Vladimir] Putin, and Russia wanting to control its border areas,” said Bo Stafanusson, the owner. “They’re looking for places to hide and land their craft off out coast – it’s a useful point for them, close to the Nato countries.”

Yet Mr Stefanusson said he also suspected it could be a “budget-submarine” – a tongue-in-cheek Swedish term for a submarine sighting that conveniently coincides with the government setting its new budget, including allocations for defence.

Some of the drama was also dampened on Tuesday when a suspicious man in black spotted wading off an island in the archipelago turned out not to be an exhausted Russian frogman emerging from the depths. He was, in fact, a Stockholm pensioner doing a spot of trout fishing.