These are big boats that swim under the sea. 
These are big boats that swim under the sea. 
Some boats have two hulls. This helps them stay afloat more easily.
These boats can carry many things. They can use tubes to launch tools. Some tools can even be sea mines.
Newer boats are made to be even quieter. They have more space to help with this. This makes them very good at hiding.
Some of these boats are still working today. They travel far away in the deep ocean.
The Akula class is a group of Russian submarines. 
These boats use a double hull system. This means they have two outer layers. One layer is a pressure hull to keep the crew safe. The other is a light hull on the outside. This design helps the boat stay afloat better.
To stay hidden, these boats must be quiet. Some versions are much quieter than the first ones. For example, the Akula II is longer. It has more space to help reduce noise. The Akula III is also very advanced. It uses even more ways to lower noise.
These submarines have many tools. They use sonar to find things in the water. Sonar is a way to use sound to see. They also have tubes to launch torpedoes. These tubes can hold different types of weapons. Some boats can even use them to plant sea mines.
The Akula class is a group of powerful Russian submarines. 
These submarines use a special double hull system. There is an inner pressure hull to keep the crew safe. There is also an outer "light" hull. This design gives the boat more reserve buoyancy. Buoyancy is the ability to float in water. This shape also gives designers more freedom. On top of the rudder, there is a bulb. This bulb holds a towed sonar array when it is pulled in.
Building these boats has changed over many years. There are four different versions of the Akula. The first was the original Project 971. This group had seven boats commissioned between 1984 and 1990. The second group is the Improved Akula I. These six boats are much quieter than the first ones. The third version is the Akula II, called Project 971U. The final version is the Akula III, or Project 971M. 
Many specific facts help us understand these ships. The Akula II, named K-157 Vepr, is very long. It displaces about 700 tons more than the Akula I. This extra space helps with noise reduction. The Akula III, named K-335 Gepard, was commissioned in 2001. It was the first boat commissioned after the Kursk disaster. This event was a very important moment for the Russian Navy.
These submarines are built to be very quiet. Staying quiet helps them stay hidden in the ocean. Some noise reduction came from a famous event. A Japanese firm called Toshiba sold special tools to the Soviets. These tools helped build more accurate propellers. This was known as the Toshiba–Kongsberg scandal. 
The Akula class is a series of fourth-generation nuclear-powered attack submarines (SSNs). In the West, they are known by the NATO reporting name Akula, which means "shark" in Russian. The Russians officially designate these vessels as Project 971 Shchuka-B. 
To remain hidden, these submarines must be extremely quiet. Many Akula units utilize a wake detection system (SOKS) consisting of hydrodynamic sensors. These sensors detect subtle changes in water temperature and salinity. They are placed at specific locations: the leading edge of the sail, the outer hull casing in front of the sail, and the bottom of the hull forward of the sail. The Akula's ability to stay quiet was significantly aided by the Toshiba–Kongsberg scandal. In the 1980s, a Japanese firm named Toshiba sold specialized nine-axis milling equipment to the Soviet Union. This equipment, along with computer controls from the Norwegian firm Kongsberg Vaapenfabrik, allowed for the production of more accurate and quieter propellers. This technology helped the Soviets close the gap in acoustic stealth.
There are four distinct versions, or "flights," of the Shchuka-B series. The first is the original Project 971, known as Akula I. Seven of these boats were commissioned between 1984 and 1990. The second version is the Project 971Is, or Improved Akula I. Six of these boats were commissioned between 1991 and 2009, and they are notably quieter than the originals. 
The Akula II and Akula III represent significant engineering leaps in size and quietness. The Akula II is longer than the Akula I. It has a submerged displacement that is approximately 700 tons greater than the original model. This extra space was used specifically for additional quieting measures. The Akula II, K-157 Vepr, was famously quieter than the latest U.S. attack submarines of its time. The Akula III, the K-335 Gepard, is even larger. It features an enlarged sail and a different towed-array dispenser on the vertical fin. The Gepard was the most advanced Russian submarine before the introduction of the Oscar II and Borei classes.

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