How fast is a nuclear submarine

Weapons technology: submarine races through the sea at racing car speed

When the peregrine falcon races down at over 180 kilometers per hour, the only thing that remains for the fish is astonishment. Because water is denser than air. It doesn't move as easily in it as it does between heaven and earth. The speed records of marine life are therefore around 100 kilometers per hour, and even those are only reached by very few swordfish and sailfish. And for human engineers and physicists it is clear that the speed of sound (which underwater at 5,328 kilometers per hour is almost five times as high as in the air) is absolutely unattainable for underwater vehicles.

But at least three-digit pace values ​​are now within reach. As early as 1977, the Soviet Union developed an almost three-ton torpedo called Shkwal (Russian: storm gust) that whizzed through the water at over 350 kilometers per hour, US technicians later developed an underwater projectile that could even be accelerated to the speed of sound. Both models, of course, had the catch that they could not be controlled.

The shipbuilder Electric Boat is currently making a name for itself in the USA. On behalf of the US Department of Defense, he developed a propulsion system that allows seasoned and controllable submarines to accelerate to Formula 1 speed. In the spring, a $ 26 million prototype is due to make its maiden voyage off Rhode Island. The planned top speed is 100 knots, i.e. over 180 kilometers per hour. There is still a lot missing about the speed of sound, but it is already a multiple of the 50 kilometers per hour that a nuclear submarine can achieve on the speedometer.

These new high-speed values ​​are made possible by a physical principle that is actually anti-tempo, namely cavitation. The term comes from the Latin cavitare (to hollow out) and describes the formation of bubbles in a liquid. And not only when it is boiling, but also when it is being stirred. The ship's propeller on the front of the blade lets the pressure of the water drop so far that its molecules no longer stick together and drift apart. Bubbles form, which implode even with the slightest increase in pressure and thus damage the screw and hull.

Not to mention that their constant ups and downs block the propulsion. In extreme cases, the vortex can even cause the screw to lose contact with the water and spin as if idling. "For a long time, cavitation was therefore considered harmful and undesirable in shipping," explains hydromechanic Yuriy Sawchenko from the National Academy of Sciences in Kiev. However, if you “inflate” the bubble effect to supercavitation, so that the whole body is enveloped by an air bubble, you would have the opposite effect: the resistance drops and the accelerated object drills through the water in the air cushion like a hot needle through the Butter. This could also be used to penetrate the speed dimensions of airplanes. The only problem is: How do you manage to constantly enclose the object with an air bell?

The Kiev hydromechanics were the first to come up with a solution in the late 1970s. First they accelerated a torpedo in a launch tube to 180 kilometers per hour, because that is the minimum speed required to form a large cavitation bubble. Then a rocket engine ignited in the torpedo in order to accelerate further. In addition, the exhaust gases from the rockets were diverted in such a way that they could “feed” the cavitation bubble directly.

The torpedo was almost completely submerged in air, only its flattened tip was in contact with the water. This enabled it to achieve enormous speeds, but it could not be steered - and the recirculation of the gas also created explosive mixtures. When the Russian submarine “Kursk” with over 100 people sank in the ocean in August 2000, those responsible refused any help from abroad. Whereupon rumors arose that the "Kursk" had been on the way for tests with supercavitation torpedoes. One of them would have exploded when it was fired - and they wanted to keep this mishap a secret.

To this day, maneuverability is one of the big problems with new underwater razors. “You can't do anything with conventional rudders, because they would have to protrude from the air bubble - and your material wouldn't last long,” explains American hydromechanic Ivan Kirschner. The German missile specialist Diehl developed a movable nose tip for steering, because it is the only point in contact with the water.