Key Points and Summary – In a legendary 2005 wargame, the small Swedish diesel-electric submarine HSwMS Gotland repeatedly slipped through the U.S. Navy’s most advanced defenses and simulated the sinking of the $6 billion aircraft carrier USS Ronald Reagan.
-The key to its success was its revolutionary Air-Independent Propulsion (AIP) system, which allows for weeks of near-silent, submerged operation.
(September 24, 2021). The navy’s only forward deployed aircraft carrier USS Ronald Reagan (CVN 76) transits the South China Sea. Reagan is attached to Commander, Task Force 70/Carrier Strike Group 5 conducting underway operations in support of a free and open Indo-Pacific. (U.S. Navy Photo by Mass Communication Specialist 1st Class Rawad Madanat)
-The shocking result was a “strategic thunderclap” for the Pentagon, exposing a critical vulnerability and forcing a complete reevaluation of its anti-submarine warfare tactics.
-The U.S. was so humbled it leased the submarine for two years to study its secrets.
The U.S. Navy Spent $6 billion on an Aircraft Carrier to Be ‘Sunk’ By a $100 Million Sub
In the complex and brutal calculus of modern naval warfare, the American nuclear-powered aircraft carrier has long been the undisputed queen of the chessboard.
It is a 100,000-ton instrument of national will, a floating fortress that projects more military power than most nations possess.
Protected by a multi-billion-dollar strike group of cruisers, destroyers, and nuclear attack submarines, it is considered by many to be an untouchable asset, the ultimate symbol of American hegemony.
PHILIPPINE SEA (Feb. 5, 2024) The Nimitz-class aircraft carrier USS Theodore Roosevelt (CVN 71) transits the Philippine Sea, Feb. 5, 2024. Theodore Roosevelt, flagship of Carrier Strike Group Nine, is underway conducting routine operations in the U.S. 7th Fleet area of operations. An integral part of U.S. Pacific Fleet, U.S. 7th Fleet operates naval forces in the Indo-Pacific and provides the realistic, relevant training necessary to execute the U.S. Navy’s role across the full spectrum of military operations – from combat operations to humanitarian assistance and disaster relief. U.S. 7th Fleet works together with our allies and partners to advance freedom of navigation, the rule of law, and other principles that underpin security for the Indo-Pacific region. (U.S. Navy photo by Mass Communication Specialist 2nd Class Andrew Benvie)
But in 2005, in the deep, cold waters of the Pacific Ocean, this entire assumption was shattered.
In a wargame that would become the stuff of naval legend, a single, tiny, diesel-electric submarine from Sweden accomplished the unthinkable.
The HSwMS Gotland, a vessel costing a mere $100 million by estimates at the time, repeatedly slipped through the most sophisticated anti-submarine warfare (ASW) screen on the planet and, in simulated combat, sank the $6 billion USS Ronald Reagan.
Submarine vs. Aircraft Carrier
This was not a fluke or a lucky shot.
The sinking of the Reagan was a strategic thunderclap, a deeply shocking and humbling event that sent shockwaves through the highest levels of the Pentagon.
It was a brutal lesson in the changing nature of undersea warfare, a stark demonstration that in the silent world of the deep, a new kind of predator had arrived.
The event served as a wake-up call, exposing a dangerous vulnerability in America’s naval defenses and proving that a small, technologically advanced adversary could put our most valuable assets at risk.
The Ghost in the Machine: Air-Independent Propulsion
To understand how the Gotland achieved the impossible, you must first understand the revolutionary technology that makes it one of the stealthiest submarines ever built: its Air-Independent Propulsion (AIP) system.
For a century, conventional diesel-electric submarines have been constrained by a fundamental weakness. While exceptionally quiet when running on batteries, they had to surface or use a snorkel to run their diesel engines and recharge, a process that made them noisy and highly vulnerable to detection. Nuclear-powered submarines solved this problem with nearly limitless underwater endurance, but their reactors and turbines, even with the best sound-damping technology, produce a constant, low-frequency acoustic signature from their cooling pumps.
The Gotland represents a third way. Its Kockums-built Stirling engine AIP system is a technological marvel. In simple terms, the Stirling engine uses liquid oxygen and diesel fuel in a closed-cycle combustion process to generate electricity. This allows the submarine to run its electric motor and recharge its batteries while remaining completely submerged. The process is nearly silent and, crucially, vibration-free. Unlike a nuclear reactor, it does not require a constant flow of noisy pumps, and unlike a standard diesel engine, it does not involve the explosive clamor of internal combustion.
The result is a submarine that can combine the best of both worlds. It can operate with the ghost-like silence of a battery-powered submarine, but for weeks at a time instead of mere hours or days. It can lurk in shallow, acoustically cluttered coastal waters where a large nuclear submarine would struggle to operate, waiting patiently for its prey. In the silent world of undersea warfare, the Gotland is a black hole, a predator that simply disappears.
The Hunt for Aircraft Carrier Ronald Reagan: A Masterclass in Stealth
The 2005 exercise was designed to test the capabilities of a modern Aircraft Carrier Strike Group against the growing threat of advanced diesel-electric submarines.
The USS Ronald Reagan and its escorts—a formidable screen of destroyers, frigates, and Los Angeles-class nuclear attack submarines—were tasked with a simple mission: find and kill the Gotland.
The U.S. Navy had taken the extraordinary step of leasing the Swedish submarine and its expert crew for a full two years, bringing it to San Diego to serve as a dedicated opposing force. They wanted to understand this new threat and develop countermeasures. They knew what they were looking for. They had the most advanced passive and active sonar systems in the world. They had helicopters dropping sonobuoys and maritime patrol aircraft scouring the ocean. And still, they couldn’t find it.
The Gotland, under the command of its wily crew, played the role of the aggressor to perfection. It utilized its AIP system to remain submerged and undetected for days, moving slowly and silently through the water, a ghost in the strike group’s defensive screen. It repeatedly slipped past the escort ships, penetrated the inner defensive zone, and put itself in a perfect firing position.
The results were devastating. Over the course of the exercise, the Gotland was credited with multiple torpedo hits on the Ronald Reagan, enough to sink the supercarrier several times over. The Swedish crew, to add insult to injury, even managed to take periscope photographs of the carrier, clear evidence of just how close and undetected they had been.
It was a masterclass in undersea warfare, a demonstration that in the right hands, a technologically advanced conventional submarine could be a carrier-killer.
A Humbling Lesson: The Aftermath
The sinking of the Reagan was a deeply humbling experience for the U.S. Navy. It was a stark and undeniable demonstration that our Cold War-era ASW tactics, designed to hunt loud, deep-diving Soviet nuclear submarines, were dangerously inadequate against the new generation of ultra-quiet AIP-equipped boats.
The event triggered a profound and necessary reevaluation of naval strategy. It spurred a massive investment in new ASW technologies, from more sensitive sonar arrays to advanced detection algorithms and unmanned underwater vehicles. It forced a shift in training, creating a new sense of urgency and respect for the threat posed by conventional submarines.
The legacy of the Gotland’s triumph is a crucial one. It is a reminder that in warfare, technological innovation can often upset the established order. It proved that a smaller, more agile, and technologically advanced force can pose a mortal threat to even the most powerful assets. The silent predator from Sweden did more than just win a wargame; it changed the way the world’s most powerful navy thinks about the war beneath the waves.
About the Author: Harry J. Kazianis
Harry J. Kazianis (@Grecianformula) is Editor-In-Chief and President of National Security Journal. He was the former Senior Director of National Security Affairs at the Center for the National Interest (CFTNI), a foreign policy think tank founded by Richard Nixon based in Washington, DC. Harry has over a decade of experience in think tanks and national security publishing. His ideas have been published in the NY Times, The Washington Post, The Wall Street Journal, CNN, and many other outlets worldwide. He has held positions at CSIS, the Heritage Foundation, the University of Nottingham, and several other institutions related to national security research and studies. He is the former Executive Editor of the National Interest and the Diplomat. He holds a Master’s degree focusing on international affairs from Harvard University.
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