Marking national day on Wednesday, Sweden called up 22,000 reservists for an exercise of a scale not seen in 40 years as tensions simmer between the West and Russia.
A total of 40 battalions are carrying out nationwide snap drill manoeuvres to ramp up military security at a time when once cordial post-Cold War relations with Moscow have cooled.
The army hopes at least half of Sweden's reservists will respond to the first mass call-up since 1975 for primarily land-based surveillance, defence and logistics tasks.
"Our mission is to strengthen Sweden's military defence and improve our operational capabilities," said Sweden's Supreme Commander Micael Byden.
"We are testing the chain of mobilisation for around half our organisation, something we have not done since 1975," Byden said in a statement.
He described the reservists as "crucial to allow the remainder of the armed forces to defend Sweden" and concentrate on frontline duties.
The Swedish government last month issued an emergency pamphlet to prepare citizens in the event of war, natural disaster or cyber attack.
Titled "If Crisis or War Comes", the brochure -- Sweden's first since 1961 -- contains advice on how to take shelter, what foods to store and what information to trust amid heightened concern about Moscow's military ambitions and intentions.
Russia does not share a border with non-NATO member Sweden, but it has a naval base just across the Baltic Sea in the Kaliningrad region.
Sweden, which has not seen armed conflict on its territory for two centuries, slashed military spending at the end of the Cold War, but was rattled by Moscow's annexation of Crimea.
Stockholm expelled a Russian diplomat in March in line with an international response to the nerve agent poisoning of Russian former double agent Sergei Skripal and his daughter in England, which the British government blamed on Moscow.
This week Swedish leaders warned of possible Russian interference ahead of September parliamentary elections.
Stockholm announced last year it would reintroduce compulsory military service as early as this summer, seven years after it was abolished.
The nation also recently resumed military activities on Gotland, an island in the Baltic.