Within the modern naval warfare scenario, Sweden’s Gotland-class submarines have turned into very dangerous opponents, almost defying even the largest naval forces in the world. Their diesel-electric submarines have indeed become legends with advanced AIP systems in many a war game. The most famous was the 2005 exercise during which the HMS Gotland “sank” the USS Ronald Reagan brand-new aircraft carrier worth $6.2 billion.
The first to enter service, in 1996, with a Stirling engine AIP system, was the Gotland-class submarines. This allows submarines to remain submerged for up to two weeks, surfacing far less frequently than earlier generations of submarines and thus greatly reducing their vulnerability. Using liquid oxygen, the Stirling charges the submarine’s seventy-five-kilowatt battery, allowing the Gotland to cruise at an average speed of six miles per hour underwater or sprint up to twenty-three miles per hour if needed.
During the 2005 war game, the Gotland was able to get away and avoid Reagan’s anti-submarine defenses, which included numerous ships and aircraft operating a fleet of sensors. Not once did it get detected as it made several attack runs on the carrier. According to naval analyst Norman Polmar, the Gotland “ran rings” around the American carrier task force; another source noted that U.S. anti-submarine specialists were “demoralized” by the experience.
The Gotland-class submarines come with many features that enhance their stealth. Twenty-seven electromagnets are installed to cancel their magnetic signature from Magnetic Anomaly Detectors. Their hulls have sonar-resistant coatings while the towers are covered with radar-absorbent material. Rubber acoustic-deadening buffers also cover the interior machinery, reducing their detectability through sonar. The submarines are also very agile; the six combined maneuvering surfaces on their X-shaped rudder and sail allow them to operate near the sea floor and make tight turns.
It was the U.S. Navy that understood the challenge these submarines presented and leased the Gotland, along with its crew, to conduct antisubmarine exercises for two years. These exercises produced convincing proof that the undersea sensors of the U.S. Navy still had a lot to contend with vis-à-vis the new stealthy AIP boats. There is an important implication here: other countries, including China and Russia, are also developing and fielding AIP-powered submarines.
As it happens, China has two diesel submarine types making use of Stirling engines. Specifically, there is a Type 039A Yuan class and a Type 032 Qing-class vessel with the capability to stay underwater for thirty days. Russia for its part has designed the Lada-class Sankt Peterburg that uses hydrogen fuel cells to power this vessel.
The obvious attractions of those inexpensive and stealthy diesel submarines notwithstanding, the U.S. The Navy has no plans to return to diesel submarines but instead is wedded to nuclear subs with multibillion-dollar price tags. Diesel submarines are ideal for patrolling waters close to friendly shores; U.S. subs, however, often have to travel thousands of miles to get to their operational areas and sometimes stay on deployment for months. Only the most advanced diesel submarine would be capable of covering that sort of distance, and it would need frequent refueling at sea to sustain a long deployment.
The development of inexpensive, stealthy, and long-enduring diesel submarines like the Gotland class is just another thing that puts carriers and other pricey surface warships increasingly more in jeopardy when they operate close enough to defended coastlines. Although diesel submarines may be wonderful in defending littoral waters, their role in blue water naval forces far away from home is not so clearly defined. The Gotland-class submarines did prove, however, that even the mightiest naval forces are made to adapt to the shifting landscape of undersea warfare.