How two stealth submarines avoid a collision

Stealth submarines are hard to find

Military submarines are built to navigate the oceans as invisibly as possible - undetected by enemies, opponents and spies. They rarely show up to make radio or telephone contact with their headquarters and otherwise mostly remain silent.

Of course, this no longer applies in an emergency. The crews then have to draw attention to themselves: They can send emergency signals on the surface of the water or give knock signals or other acoustic signals under water.

In doing so, however, the design of their submarines may get in the way, because it is designed so that as many signals as possible are swallowed.

Is ARA San Juan even a stealth submarine?

Modern stealth submarines are class A212 of the German Navy or the Saab A26 of the Swedish Navy. These types of submarines were developed in the 1990s and have been designed from the start as completely stealth submarines. They make hardly any noise, hardly radiate heat and only reflect radar and sonar pulses minimally. The Argentine submarine ARA San Juan cannot be compared with such submarines.

This submarine was built by the German shipyard Thyssen Nordseewerke and put into service in 1985. It later received another modernization that was completed in 2013.

What does "invisibility" mean on a submarine?

In principle, every military submarine is designed in such a way that it sends out as few signals as possible - of course, this also applies to ARA San Juan.

As early as World War II, Germany was building submarines with stealth capabilities. Class VII of the German Navy is considered the first such submarine. With this type of submarine, the aim was to reduce the engine noise as much as possible and to generate the weakest possible radar signal when traveling over water. Since then, submarine designers have always developed new ways to make the boats "invisible". Here are the most important tricks:

A stealth bomber can hardly be seen with radar due to the angle of the wing

Scattering and deflection of waves - instead of reflection

The greatest danger to ships and aircraft - but also to submarines - comes from radar. It works in such a way that electromagnetic waves are reflected and thrown back by a solid, preferably metallic, material. Yachts made of fiber-reinforced plastic reflect only weakly and are actually also stealth ships. Only that is not wanted here. That is why they usually have a radar reflector on the mast - an octahedron made of sheet metal. This makes the ship visible to the radar.

Designers who want to make a large ship invisible use plastic surfaces in a similar way. They should scatter the radar waves in all possible directions instead of reflecting them directly.

And they build the walls of ships or airplanes at a peculiar angle, which means that the signals are radiated in a different direction. This trick is used less often in submarines. The more important is the optimal streamline shape: the better the submarine glides, the less engine noise and heat is emitted.

In stealth ships, designers change the angle of the outer walls to fake radar signals.

Avoid magnetism

Nowadays only non-magnetic materials such as stainless steel or titanium are used in military submarines. This has to do with the fact that many sea mines have magnetic detonators. If a ship comes too close to them, they explode.

If the submarine is not magnetic, however, there is a high probability that it will be able to glide past a sea mine undamaged. This is also an advantage to avoid other electromagnetic detectors.

Sound-absorbing materials outside ...

What applies to radar waves also applies to noise. The most important instrument for searching the sea bed is the sonar, also known as an echo sounder. It emits a sound, which is then reflected off the ocean floor and comes back. Depending on how long this takes and how clear the signal is, the sonar device can detect how deep the water is and whether the bottom is rather sedimentary, overgrown or rocky.

Here, too, a suitable surface material absorbs a large part of the sonar signal. The submarine may then only look like a somewhat diffuse heap of mud on the screen.

... and inside

Of course, the enemies should not be able to hear what is going on in the submarine either. Even a slamming hatch or a rattling pot could give away the submarine. Engine and drive noises are even clearer.

To do this, everything inside a submarine that could somehow hit each other is insulated and padded with rubber. Only the quietest motors are used and only whisper-quiet electric motors for secret diving trips.

The good noise insulation also makes it difficult for the team to make themselves noticeable by knocking signals.

As little heat and other radiation as possible

U-boats can also be recognized by the heat they produce - for example with an infrared camera from an airplane. The designers therefore try to keep the heat from the engines in the submarine as much as possible or at least dissipate it as well as possible.

In any case, there should be no areas in which the water leaks particularly hot. The most effective measure here too: highly efficient motors.

Vehicles, planes and ships can also betray themselves by electromagnetic waves that they emit themselves. Of course, this also applies to submarines. These can be radio signals but also other radiation emitted by electrical devices on board: Own radar systems, computers, motors, cell phones, weapon systems and much more.

All of these radiation sources must be turned off best or. where that doesn't work - at least as well shielded as possible.

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