5 Fastest Submarines, Ranked By Top Speed

Submarines have grown into a vital component of any world power's navy as they can traverse the planet's oceans without drawing attention. With modern nuclear technology, they can remain at sea virtually indefinitely, using atomically generated steam to power the turbines that turn the propellor. 

Submarines need to exhibit two main traits for a navy to purchase them. First and foremost, they need to be stealthy. Along with bombers and land-based missiles, submarines act as a leg of the U.S. nuclear triad, where stealth is paramount. If their locations were discovered, it could cripple the country's security. Moreover, attack subs rely on silence to watch their rivals and get the upper hand if they enter combat.

Another trait submarines need is speed. They're far from the fastest vessels in the world's oceans – five of the fastest navy ships exceed 40 knots — but speed is a necessity in order to escape detection and attack. If a submarine can travel fast, it also can close the distance on enemy ships quickly, letting it get in and out for an attack. And if it can dive fast, it can avoid most anything from the surface. Combining speed and stealth makes for a lethal ship. So here are the fastest submarines ever.

The USS Seawolf and its two highly advanced sister submarines changed underwater warfare forever when they entered active duty in 2001. They perform some of the U.S. military's most covert operations, gathering intelligence and keeping an eye on American adversaries throughout the world. A GE PWR S6W nuclear reactor powers this class of submarine, generating 52,000 horsepower through two steam turbines. This power gets the submarine class up to speeds that exceed 25 knots (roughly 28 mph) while submerged.

Lt. Cmdr. Bob Aronson, USS Seawolf's executive officer in 1998, soon after it was commissioned, told Popular Mechanics, "At 25 knots, our boat is quieter than the last Los Angeles-class submarines sitting at the pier." That's quite the testimony for a submarine that relies on silence to do its job. It has likely kept other nations' submariners up at night. It's a shame the U.S. Navy never purchased more than three. 

There's no publicly accessible document stating an official top speed, a detail likely kept hidden for national security reasons, but it's believed these fast attack subs can get up to 35 knots (40 mph), which would put it higher on this list — in the same class as Russia's Yasen-M-class nuclear submarine. Being able to reach 35 knots is beneficial for attack submarines because that speed would let them evade pursuers in the highly unlikely event that they're ever detected. 

Sitting at 318 feet (97 meters) long with a displacement of 8,157 tons, the Astute-class attack submarine is the largest sub ever employed by the Royal Navy. It's also one of the fastest in the world, capable of reaching 30 knots (34.5 mph) hile submerged. With the Rolls-Royce PWR 2 pressurized water reactor powering Astute subs, they can theoretically sail around the planet indefinitely. Their cores won't have to be refueled during their service life. A need to replenish food stores after 90 days is essentially the only constraint bringing these subs back into port. Well, that and the crew's sanity.

Astute-class subs have six torpedo tubes they fire Spearfish torpedoes from. These torpedoes can target adversaries up to 40 miles away and with their 660 pounds of explosives, they can make easy work of most vessels they encounter. If given the go ahead to strike a land target, there's the Tomahawk IV missile whose range exceeds 1,000 miles. The sub can then use its top speed to race away from where it fired, like a phantom in the water.

Submarines are perfect vessels for special forces teams to deploy from as the subs can sneak up to enemy territory. For that, the Royal Navy subs have a dry deck shelter where Royal Marine Commandos can deploy from while the submarine is submerged.

Overall, the U.S. maintains superiority with its large submarine fleet, but China has been hard at work to improve its capabilities and close the technological gap between it and other armed forces. Chinese scientists believe they can make submarines fast enough to outrun incoming torpedoes with laser propellors, according to Popular Mechanics, but they're not quite there yet. The People's Liberation Army Navy currently has two generations of the Shang-class attack submarine in its service (Type 093 and Type 093A), with a third in the works (Type 093B).

Currently, the Type 093A subs are the most modern China has in use. These nuclear-powered attack submarines keep pace with the Royal Navy's Astute class at 30 knots thanks to some upgrades in 2015, making them China's most powerful attack submarines. There are six torpedo tubes that can be loaded with various torpedo-sized weapons, including YJ-82 anti-ship missiles, rocket mines, and Yu-6 thermal and electric torpedoes. The Yu-6 thermal torpedoes are similar to America's Mk48. 

If the Shang-class subs need to go against surface vessels, they'll be armed with YJ-18 supersonic cruise missiles. There isn't a vertical launch system on the Type 093A, but it's believed that there will be on the Type 093B and it'll be capable of attacking land installations. China is more secretive than the United States with its technology, so it's unknown the type of reactor powering the Shang-class.

Yasen-M-class submarines are some of the most advanced subs under Russia's control. They're an upgrade from the Yasen class with a more efficient KTP-6 nuclear reactor. The new reactor reportedly runs more quietly than previous iterations, improving the sub's stealth and making it a bigger threat. It has a 13,800-ton displacement with a length of 426 feet. One of its more impressive assets is its ability to reach a speed of 35 knots (40.2 mph). On top of its impressive speed, it can fire multiple types of cruise missiles, including hypersonic ones that can reach Mach 9. Unlike the impressive range of the Tomahawk VI missiles used by the Astute class, though, Russia's Zircon only reaches 600 miles.

These subs' hulls are covered in rubber as a means of improving their acoustics, which some senior U.S. military officers have said puts Russia's subs on par with America's in terms of their stealth. The torpedoes they use are a big drawback, however, as they date back to Soviet days. Russia is testing new torpedoes, but for now the subs are stuck with outdated tech. Despite that, the Yasen-M-class subs are capable of anti-submarine, anti-ship, and anti-surface strikes.

The fastest submarine isn't one of the newest or most advanced nuclear submarines in the world. But K-222 – K-162 before being redesignated — was ahead of its time, and even exceeded its designers' expectations. This was a nuclear submarine commissioned by the Soviet Union in 1969, when the USSR was looking for innovation more than anything from its submarines. This led to the K-222 and a powerful nuclear pressure water reactor. Coupled with its lightweight titanium hull, the first one any sub used, it could achieve speeds nobody had seen from an underwater vessel.

During a test in 1969 it reached 42 knots when engineers thought it would make at least 38. During another test in 1971, the Soviets were able to get K-222 up to 44.7 knots (51.4 mph), breaking the world submarine speed record. 

As impressive as that was, the boat didn't last longer than two decades in service because reaching those speeds underwater required full power from the nuclear reactor, which brought with it a slew of problems. First, the hull would vibrate and generate noise that exceeded 100 decibels, negating a submarine's primary job of being quiet. At top speed, it also suffered structural damage on its hull's exterior. This prompted the Soviets to limit the sub's deployments. It was decommissioned in 1988, then 11 years later had its name stricken before being broken down in 2010.