Weapons and Kit

Sweden's silent Gotland class submarines tailor-made for protecting Baltic Sea

Watch: How Sweden's Gotland-Class submarine has redefined underwater warfare.

As Sweden hopes to soon join Nato, it could play a highly valuable role for the alliance in policing the Baltic Sea in northwest Europe.

The country's world-leading submarine fleet comprises some of the most advanced conventional submarines ever built.

Tailor-made for the Baltic Sea, which is too shallow for nuclear-powered subs, the silent Gotland-class submarine, is Sweden's prized asset.

They are the world's first diesel submarines to use an Air-Independent Propulsion (AIP) system based on the Stirling engine – where heating and cooling gases in a closed circuit can be harnessed for motion.

This AIP system, which is usually exclusive to nuclear-powered submarines, allows these vessels to stay submerged for weeks.

The Gotland-class submarine uses liquid oxygen and diesel to heat the engine and cold seawater for cooling, this expands or contracts gases in the closed engine system which pushes a piston to drive the sub's systems.

The result is an engine that is quiet, vibration-free, and without any exhaust.

A submarine powered this way has no need to snorkel or vent to recharge batteries or generate oxygen, like traditional diesel subs.

Sweden's HMS Gotland submarine during sea trials Picture Saab Kockums — HSwMS Gotland, the first ship of the Gotland-class, during sea trials (Picture: Saab Kockums).

This groundbreaking Saab AIP system significantly increases a diesel-electric submarine's underwater endurance, offering cost-effective stealth and silence when cruising below the surface.

Sweden has a distinguished history in underwater warfare and long-operated submarines to safeguard the Baltic Sea from a Russian invasion – a threat that has significantly returned following Russia's invasion of Ukraine.

Former US Submarine Commander David Marquet told Forces News: "The Gotland is a wonderful submarine, it's very quiet, it's effective, it's potent.

"It's essentially a short-range submarine, the Swedes have a problem pretty similar to what the Taiwanese have... an aggressive, highly capable, well-funded military on their doorstep, which has incurred in their sovereign waters in the past.