During the Cold War, the Soviet submarine program was a force to be reckoned with. The U.S.S.R.’s underwater killing machines captured the imagination of Westerners and Soviet citizens alike. Tom Clancy’s 1984 novel (adapted as a film the following year) The Hunt for Red October depicted a daring attempt by the crew of a fictitious Soviet Typhoon Class ballistic missile submarine to defect to the United States. In the tense years of confrontation between Washington and Moscow, many Americans imagined Soviet submarines lurking off the country’s coastlines. Submarines granted both superpowers the ability to unleash nuclear Armageddon from the quiet sanctuary of the ocean depths.

After the collapse of the Soviet Union, the Russian submarine program fell into decline along with many other branches of the Russian military. In the past decade, however, Russian officials have undertaken efforts to modernize their armed forces. From upgrading Cold War models to meet present-day challenges, to designing completely new platforms like the Borei and Yasen Class submarines, Russia is clearly determined to renew the status and capabilities of its underwater fleet.

Here are the five submarines that deserve particular attention.

Akula Class Submarine

Built in the Soviet Union as the Bars Class 971, this nuclear-powered attack submarine is better known by its NATO reporting name “Akula.” While the Akula cannot run as quietly as some of its Western counterparts, it remains a credible threat, especially after a series of upgrades in the aftermath of the Cold War.

The Soviet Navy commissioned seven Akula I models between 1986 and 1992. Between 1992 and 1995, Russia commissioned between two and four upgraded Akula I subs. Moscow had already set about designing a more comprehensive upgrade, dubbed Project 971A—the Akula II. This upgrade featured an extended hull length of 110 meters and an improved displacement of 12,770 tons. The enhanced design also incorporates a quieter engine than its predecessors, making the Akula II Russia’s quietest submarine design. Russia built three such vessels: the Viper (commissioned 1995), the Nerpa (2000), and the Gepard (2001). Moscow is expected to keep the Gepard in its arsenal until at least 2025 while the Nerpa is being leased to India.

For surface cruising, the Akula reaches speeds of up to 10 knots. Once underwater, this submarine can achieve speeds of up to 33 knots while diving as far as 600 meters. Once deployed, the Akula has an endurance of 100 days. The Akula is armed with a variety of anti-ship, anti-sub, and anti-surface weapons, allowing it to complete a range of missions. One Akula class submarine can carry as many as 12 Granit cruise missiles, which come in anti-ship and land attack variants. The Granit missile has a range of 3,000 kilometers. For anti-ship and anti-sub operations, the Akula I has eight torpedo launch tubes, while the Akula I Improved and Akula II have ten. The Strela SA-N-5/8 portable launcher with 18 missiles gives the Akula class an anti-air capability as well.

Kilo Class Submarine

Conceived during the Soviet era at Rubin Central Maritime Design Bureau at St. Petersburg, Russia’s Project 877 Paltus (NATO reporting name “Kilo”) is a diesel-electric powered attack submarine. First commissioned by the U.S.S.R. in 1982, the Kilo remains in service in Russia and around the world.

The Kilo is a smaller submarine, with the Iranian version boasting an underwater displacement of 3,076 tons and hull length of 70 meters. The basic Kilo model contains six torpedo launch tubes. This platform can be used for systems like the TEST-71MKE TV electric-homing torpedo, which carries a 205 kilogram explosive charge. The Kilo can also release up to 24 mines. Eight anti-aircraft missiles can be fitted to the Kilo, which is compatible with both the Strela-3 and Igla surface-to-air systems. India, which also uses the Kilo, contracted the Russian shipyard Zvezdochka to add anti-ship missiles like the Klub S (range: 220 kilometers) to its models.

The Kilo’s diesel generators give the submarine a speed of up to 10 knots for surface cruising and 17 knots submerged. The Kilo can dive as far as 300 meters below the waves and has an endurance of 45 days. Post-Soviet Russia still uses the Kilo, while the model is also in service in countries like China, India, Iran, and Algeria. Two ex-Warsaw Pact NATO members, Poland and Romania, also use the Kilo.

Type 636.3 Varshavyanka (Improved Kilo)

When Russia’s new diesel-electric Lada submarine failed its sea trials in 2010, Moscow turned to a Cold War classic: the Kilo. To fit the niche for a modern diesel-electric attack sub, Russia set about upgrading the earlier Kilo model.

Enter the Type 636.6 Varshavyanka, also known in the West as the “Improved Kilo.” Originally intended as an intermediate step between the original Kilo and the Lada, the Varshavyanka will have to fill the gap until the new models are deemed seaworthy. The Russian Navy commissioned six such vessels, four of which have been launched. The newest, Krasnodar, was launched in April 2015.

With a displacement of up to 4,000 tons submerged, the Varshavyanka serves as a platform for a powerful weapons suite. Like its predecessor, the Improved Kilo has six torpedo launch tubes and is armed with surface-to-air missiles like the Strela-3 and Igla. The newer Type 636.6 model also carries anti-ship missiles like the Novator Club-S. This missile, tipped with a high-explosive warhead, has a range of 220 kilometers.

Like the original Project 877, the upgraded Kilo has an endurance of 45 days and a maximum diving depth of 300 meters. The Improved Kilo boasts higher speeds than its predecessor: 11 knots at the surface and 20 knots underwater. A silent killer, the upgraded model is already viewed as one of the quietest diesel-electric submarine models in service. Still, the Rubin Design Bureau is exploring ways to fit the Varshavyanka vessels with an Air-Independent Propulsion system, which has the potential to run quieter than even a nuclear power plant.

Borei Class Submarine

The first completely new Russian submarine model designed since the fall of the Soviet Union, the Borei Class is a series of nuclear powered ballistic missile submarines. The lead ship in this new class, the Yury Dolgoruky was launched in 2008 and commissioned in 2013. A second Borei class sub was launched in 2010 and commissioned in 2013. A third was launched in 2012, while the newest vessel, the Knyaz Vladimir, was laid down earlier that year. Moscow hopes to replace its aging fleet of Soviet-era Typhoon and Delta III submarines with the new Borei class model.

The Borei Class hull length is 170 meters, and each submarine has a submerged displacement of 24,000 tons. Yury Dolgoruky and its sister vessels carry 16 RSM-56 Bulava submarine-launched ballistic missiles. Bulava missiles are tipped with a 150 kiloton yield nuclear warhead and have a range of 8,000 kilometers. Some reports indicate the RSM-56 may have a longer range and more destructive capability: up to 10,000 kilometers and a 500 kiloton yield. In addition to its ballistic missile payload, the Borei Class craft also come with six torpedo launch tubes, which can be fitted with a range of anti-submarine warfare torpedoes.

The nuclear power plant onboard Borei Class submarines grants the vessels a surface speed of 15 knots and a submerged speed of 29 knots. The vessels have a maximum diving depth of 480 meters and an endurance of 100 days. Borei Class submarines promise to provide the Russian Navy with a potent long-range capability for years to come. Already, Moscow has placed an order to receive 10 new vessels by 2020.

Yasen Class Submarine

Sevmash Shipyard’s Project 885 Yasen is Russia’s response to an aging fleet of Akula class submarines. This nuclear powered model will eventually replace Soviet-era designs and service Moscow’s need for a capable attack submarine. The first Yasen class sub, the Severodvinsk, joined the Northern Fleet, based in Severomorsk, in 2014.

Yasen class submarines have a hull length of 111 meters and an underwater displacement of around 13,500 tons. Each Project 885 vessel can carry weapons designed to hit land targets, surface craft, and other submarines, allowing the Yasen class to carry out a range of missions. To conduct anti-submarine operations, the Yasen class comes equipped with eight torpedo launch tubes and can fire ASW missiles like the long-range supersonic P-800 Oniks.  Oniks missiles can also be deployed as an anti-ship weapon. For targets on land, the Yasen Class submarines can launch 3M51 cruise missiles, which can be tipped with a nuclear warhead. 3M51 missiles have a range of 800 kilometers.

The powerful nuclear propulsion systems onboard Yasen class submarines allow the new models to greatly outpace their predecessors. Project 885 subs can achieve speeds of 20 knots at the surface and 35 knots submerged. Yasen class vessels can slip over 600 meters beneath the waves, rendering them an ever more potent threat to Russia’s rivals.

Evans Gottesman is a research assistant at The National Interest.