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There are also fears that the Russians might use a port they lease on the strategically important island of Gotland, which military sources have indicated has been deepened to allow warships to anchor.
The Swedes are also bracing themselves for threats of nuclear attack from President Vladimir Putin with the Stockholm government increasing provision for civil defences.
People around the capital are stocking up on food, water and fuel in preparation for a potential major cyber strike, shortly after Sweden announces its application, which is expected on Sunday. Neighbouring Finland is also due to announce its decision on requesting Nato membership within days.
Dr Gunilla Herolf, of the Swedish Institute of International Affairs, told The National that the threat was being taken seriously.
“The Russians will not respect the territory of Sweden,” she said from Stockholm. “They will see to it that on day one we will not be able to use credit cards or have electricity. This is what people expect and are preparing for.”
Swedes are buying special water tanks, hand-charged radios, camping stoves and extra food in the event of conflict, she said.
It is understood that the Swedish government is also making plans to refill the Vattenfall major oil reservoir and power plant that was built during the Cold War.
Sweden also fully expects to be threatened by Mr Putin with his nuclear arsenal. “I’m sure he’ll say ‘don't forget, we're a nuclear power’ and then suddenly all our cities are targeted,” said Dr Ian Anthony of the Stockholm International Peace Research Institute.
While “some sort of direct military action is unlikely”, Dr Anthony said “you can't rule anything out with Russia.”
Sweden was joining Nato because there was “no sense of trust” that Russia would respect territorial boundaries. “Russia has progressively stepped across all of the red lines we thought existed, we need to be prepared for the next phase in Europe,” he said.
A crucial reason for Sweden joining the alliance is to defend the island of Gotland, which is strategically placed in the middle of the Baltic Sea, 250 kilometres from the Russian exclave and naval base at Kaliningrad, and a centre for access to the eastern Baltic.
Gotland would also play a vital role in allowing the safe passage of Nato troops to Finland protecting sea and air transport, said Dr Anthony, who heads Sipri’s European security department. “An adversarial control of Gotland would put a big barrier in the way of reinforcements that have to come from the West through Norway.”
Swedish defence sources also indicated that the Silte harbour, which was leased to Russia as part of a gas pipeline agreement in 2016, had been deepened to take “big ships”.
“They already have the harbour and this could well be used if they want to send a lot of troops to Gotland,” an officer said. “Russia taking Gotland would significantly disrupt Nato reinforcement of troops in the Baltic states and would become a hub for surface-to-air missiles threatening all air transport.”
Sweden has already sent an infantry regiment equipped with armoured vehicles after three Russian landing ships were sent from its Arctic ports to the Baltic.
Russian fighter jets, bombers and spy planes have all breached Swedish airspace in the past year.
“There is a genuine nervousness in Sweden but we believe that nervousness will disappear once we are covered by Nato’s Article Five,” said Dr Gunilla Herolf – a Nordic security policy specialist – referring to the convention that gives automatic protection to alliance members.
She also expected Gotland to quickly fill with US and British military personnel soon after Sweden joins Nato, possibly in a matter of months.
“When we become members, Gotland will be extremely useful for defending Baltic states because it is the most essential spot.”
The sheer size of Sweden and Finland will present Nato with significant territory allowing for “strategic depth”, Dr Anthony said, and “rear area logistics reinforcement”.
Sweden is also in the early stages of restructuring its military, which has declined from a force of 100,000 to 23,000 personnel since 1995.
While the military is rebuilding, Sweden’s defence industry has “significant advanced technologies and combat capability”, with strong industrial alliances with Britain, America and Germany.
This has allowed it to jointly develop systems such as the NLAW anti-tank missile with Britain that has been used to great effect in Ukraine.
It also has the Gripen multirole warplane as well as advanced electronic warfare systems, airborne surveillance, smart artillery and counterbattery radars, all of which will prove useful to its future Nato allies.