Now that the U.S. Navy has eleven active aircraft carriers, the fleet represents a fearsome deterrent and weapon that can be deployed worldwide. However, they do make big, lucrative goals. For opponents, adding one of these behemoths to your kill count can only be described as a prize of unimaginable value that would extend far beyond the battlefield. And it happened – well, sort of. The airline in question was the USS Ronald Reagan, which thankfully is still very much with us. And the fly in the ointment responsible for the carrier was a $100 million Swedish diesel-powered submarine called the HSMS Gotland.
The Gotland, a 1,600-ton submarine, in a true David and Goliath moment, fired a barrage of torpedoes that took the 100,000-plus ton aircraft carrier to task. The good news for the USS Ronald Reagan (one of the oldest aircraft carriers still in service) is that it was just a war game from 2005 and instead of real torpedoes, the Gotland took a series of photos of the aircraft carrier. Albeit from a range that was far too close for comfort for the US Navy.
How could a diesel submarine penetrate the airline’s protection and deliver such a deadly ‘virtual’ blow? Perhaps unsurprisingly, stealth was one of the main reasons. Even more surprising, the stealth function of the submarine’s diesel engine was a crucial factor. For those of us who associate diesel engines with their distinctive ‘clang’ sound, this may seem counter-intuitive. Let’s take a closer look at the outcome of the war game that demoralized American anti-submarine specialists.
How a Swedish submarine penetrated an aircraft carrier’s defenses
It’s fair to say that the Gotland’s success in taking out Ronald Reagan sent shock waves through the US Navy. This was not an isolated incident; Over two years of war games, the submarine consistently managed to evade the layers of anti-submarine defenses protecting an aircraft carrier group. Or, inside the words from naval analyst Norman Polmar, the submarine “ran rings” around the US aircraft carrier task force. The Navy was so impressed – or depressed – that it chartered the HSMS Gotland for two years to reveal its undercover secrets.
At first glance, this might be the kind of outcome one might expect or tolerate if the attacks had been carried out by a high-tech, nuclear-powered attack submarine with a price tag that could approach $6 billion, rather than a $100 million diesel-powered submarine. Gotland-class submarines have a clever trick, however; namely the Stirling engines that produce the power, a technology that has been around since the early 19th century.
The Stirling engine in Gotland-class submarines is classified as an “Air Independent Power (AIP)” system, meaning it can remain submerged for weeks rather than days. The Stirling engine works by heating and cooling the gas in a cylinder. For cooling, the submarine uses seawater, a resource it has in abundance, and diesel is just a source of heat. This also makes it incredibly quiet. The coolant pumps required on nuclear submarines are indeed noisier. Of course, the use of radar-absorbing materials and other stealth technologies is also relevant.
The growing threat of diesel-electric submarines
The decommissioning of the USS Dolphin on January 15, 2007 marked the end of the diesel submarine era for the US Navy. Since then, the submarine fleet has relied entirely on nuclear-powered boats. At the time this was a decision that seemed logical, because what chance would a boat powered by two diesel bus engines have against the increasingly sophisticated anti-submarine warfare measures? But as Sweden’s Gotland-class submarines proved, the diesel-powered submarine was far from dead in the water; it just had to be reimagined.
Other countries also see a future in diesel-electric AIP submarines. For example, China is believed to have 48 diesel-electric submarines, 21 of which are AIP compliant. Other countries that have or are developing AIP submarines include Japan, Russia, Germany and India. While nuclear submarines are undoubtedly more advanced than their diesel counterparts, the new generation of AIP boats are more cost-effective to build and operate.
The US Navy has not committed to a return to non-nuclear submarines. However, the American Naval Institute believes there is strong evidence that these highly capable boats could be what the US Navy needs. While there are certain operational benefits that AIP submarines bring, the price tag is also a big carrot. Even a large “transoceanic” AIP submarine would cost $1.1 billion – or a quarter of a currently manufactured Virginia-class submarine. By comparison, the Gotland was commissioned in 1995 and cost about $100 million, or $213 million in today’s terms. Not bad for a boat that sank an American aircraft carrier.
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