The submarine left the entire US aircraft carrier fleet helpless.

The USS Ronald Reagan's powerful escort fleet failed to detect a small Swedish diesel submarine during a mock attack.

HSMS Gotland before sailing

In 2005, the newly built, $6.2 billion US aircraft carrier USS Ronald Reagan and its escorts participated in a mock defense exercise, their opponents beingThe light submarine HSMS Gotland was leased by the US from Sweden for a period of one year.

This light submarine was quietlybypassed the dense layers of protection of the US escort ship and continuously launched simulated torpedoes at the aircraft carrier.USS Ronald Reagan. After "sinking" the enemy ship, tThe submarine Gotland left before the American fleet even realized its presence, according toNational Interest.

The US Navy conducted several such exercises with the Gotland submarine in its first year, but each time its destroyers and nuclear attack submarines were outclassed by the tiny 1,600-ton Swedish submarine.

Too impressed with the ability to bypass the systemanti-submarine defenseequipped with many modern sensorsfrom the USS Ronald Reagan escort squadron of the submarine Gotland, hThe US Navy decided to lease the ship for another year to study its technical and tactical features.

HSMS Gotland, a Gotland-class diesel submarine, is a relatively cheap diesel submarine, costing only about $100 million, equivalent to an F-35 fighter jet. The US Navy retired all diesel submarines in 1990 to focus on developing larger, more powerful nuclear attack submarines.

In the past, diesel submarines were limited by their noisy engines and could only stay underwater for a few days before having to surface for air, making them vulnerable to detection and attack by enemy aircraft. In contrast, nuclear-powered submarines do not require large air supplies, can operate quietly underwater for months, and have higher speeds.

However, the Gotland class, launched in 1996, was the first submarine to use an air-independent propulsion (AIP) system, which reduced its dependence on external air sources. They could stay submerged for up to two weeks while maintaining an average speed of 6 mph, or use battery power to accelerate to 23 mph.

The HSMS Gotland submarine easily outmaneuvered the US aircraft carrier formation. Photo: National Interest.

Diesel engines are used when the ship is surfaced or when using snorkels. The Gotland class is much quieter than nuclear submarines, which have to use very noisy reactor cooling systems.

The Gotland submarine has several other features that make it very difficult to detect. It is equipped with 27 electromagnets, which can hide its magnetic signature from sensors that detect magnetic anomalies. Its hull is covered with sonar-resistant materials, and its conning tower is made of radar-absorbent materials.

The ship's machinery is covered with rubber cushions to reduce noise, reducing the possibility of detection by enemy passive sonar. The Gotland is extremely maneuverable thanks to six control surfaces on the X-shaped rudder and conning tower, allowing it to operate close to the seabed and perform sharp turns.

After two years of exercises, the US Navy realized that Gotland was the biggest challenge to their anti-submarine force and the undersea sensor system they were equipped with could not deal with AIP submarines.

Gotland is just one of many AIP submarines in the world. Russia and China both design and operate stealthy diesel-electric submarines, most famously Project 636.Vashavyanka (NATO designation: Improved Kilo). They have very low noise levels, are equipped with many modern technologies to help them hide under the sea, and are nicknamed "ocean black holes" by the US Navy.

Other manufacturers of AIP submarines include Spain, France, Japan, and Germany. These countries have sold submarines to many navies around the world, including India, Israel, Pakistan, and South Korea. AIP submarines have evolved into larger, more heavily armed, and more expensive types, such as the German Dolphin and French Scorpene class.

Gotland is the first class of submarines equipped with AIP technology. Photo: Wikipedia.

Diesel submarines are most effective at attacking enemy fleets when their location is known from intelligence. However, their slow underwater speed makes them unsuitable for tracking moving targets over large areas of ocean.

The advent of cheap, stealthy, long-range diesel submarines has put aircraft carriers and other expensive warships at greater risk when operating near enemy shores. AIP submarines will be an effective means of defending coastal waters, military experts say, although their role in offshore navies is unclear.

According to VNE