Summary and Top 3 Points You Need to Know: Sweden’s Gotland-class submarines, equipped with advanced air-independent propulsion (AIP) systems, have proven their stealth and effectiveness in naval warfare. During a 2005 war game, the HMS Gotland managed to "sink" the USS Ronald Reagan, showcasing its ability to evade detection by even the most advanced U.S. Navy anti-submarine systems.

-The Gotland’s success stems from its quiet AIP system, reducing the need to surface and increasing its operational stealth.

-With recent upgrades, the Gotland-class remains a formidable underwater threat, raising the question of whether the U.S. Navy should test its capabilities against the improved subs, especially as China adopts similar technology.

How Sweden's Gotland-Class Sub Sank a U.S. Aircraft Carrier in War Games

Diesel engines aboard submarines used to be considered out of date and something more in line with World War II than today's modern stealthy subs.

Not so with Sweden’s Gotland-class of subs.

These modern diesel-electric boats, now powered by air-independent propulsion (AIP),  are so quiet that the U.S. Navy took an interest and leased one of the models to conduct testing and war games.

The result: a 'dead' US Navy Aircraft Carrier.

How the Gotland Sank The USS Ronald Reagan in a War Game 

There is so much interest in the Gotland-class submarines comes mainly from a war game several years back that went very badly for the U.S. Navy.

The HMS Gotland was able to penetrate the defensive measures of a carrier strike group in 2005. The small sub got so close it produced a photo of the carrier USS Ronald Reagan near San Diego. In a naval war game such as this, it is considered a “sinking.”

The Navy liked the Gotland so much that it leased it for a second year for more simulations. Now the Chinese have the same reduced-noise technology that is proving a challenge for American undersea warfare tactics.

It’s a Robust, Multi-role Sub

The Gotland-class boats were originally designed by Saab-Kockums and commissioned in the mid-to-late 1990s. These subs can fulfill all kinds of roles - from surface-attack to killing other submarines to dropping off special operations forces personnel. There are three of the boats in the Gotland-class and they are able to sneak up on adversaries and snoop for communications and electronic intelligence.

The Gotland Kicked *** in War Games Against the U.S. Navy

The U.S. Navy, with some of the best anti-submarine ships and aircraft in the world, just could not find the Gotland in combat simulations. The relatively low-cost $100 million (cheaper than a nuclear-powered model) sub was able to sneak around at will while performing opposing force (OPFOR) maneuvers. The Gotland and the American carrier battle group, consisting of several support ships, ran the simulation over and over and the Gotland still came out on top.

What’s the Secret?

The secret to the Gotland’s low acoustic signature is the quiet Air Independent Propulsion (AIP) system of the Stirling engine. This means the Gotland does not have to surface often or use a noisy snorkel like traditional diesel boats. Instead, the Stirling engine has a 75-kilowatt battery that uses liquid oxygen. The Stirling produces speeds of 11-knots on the surface and 20-knots submerged. The Gotland just runs on AIP for weeks at a time. The Swedes were the first to employ this type of propulsion.

Run Silent and Be Hard to Find

It has 27 electromagnets designed to lower its magnetic signature. Its hull is more sonar-resistant, and the tower is made of materials with some stealth characteristics. Equipment inside is covered with rubber acoustic-deadening to reduce sonar detection.

Not a Very Big Sub

The subs are relatively small at 205-feet long, have a beam of 20-feet, and a draft of 18-feet with a displacement of 1,380 tons. The crew numbers are low and only a maximum of 32 sailors can serve on board.

Watch Out for the Torpedoes

The Gotland has two 533mm and two 400mm torpedo tubes. The Bofors Type 613 torpedoes are launched from the 533mm tubes. The Type 613 is a muscular torpedo used in surface warfare. It has wire-guidance and homes in on targets, sending a warhead of 529 pounds. The sub can also lay mines.

Gotland-class Gets Upgrades

Since the Gotland was originally produced in the 1990s, the Swedes instituted a 2020 mid-life upgrade During this time 50 systems such as navigation and sensors were newly fitted, and others changed. The next generation of the Blekinge-class will allow the subs to assess their environment with an optronic mast, which will replace the periscope.

U.S. Navy vs. Gotland: A Rematch? 

If it hasn’t already, the U.S. Navy should work with the Swedish Navy to replicate the 2005 training exercises to see if the Americans can improve their performance against the upgraded Gotland-class. This would be extremely helpful as China now has AIP technology and would surely use such submarines in a naval conflict with the U.S. Navy.

About the Author 

Brent M. Eastwood, PhD, is the author of Humans, Machines, and Data: Future Trends in Warfare. He is an Emerging Threats expert and former U.S. Army Infantry officer. You can follow him on Twitter @BMEastwood. He is presently a Senior Editor for National Security Journal.