Stealth Technology for Huge Ocean-Going Ships

This concept was invented and Engineered around 1990. This presentation was first placed on the Internet in July 1999.

A method for hiding American ships from enemy radar is presented. Enemy radar-guided missiles would be less successful in attacking a ship protected by this system.

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Around 1990, an American ship in the Persian Gulf was hit by an Exocet missile. As a result, a number of Americans died. In addition, it seemed to me to demonstrate the implicit vulnerability of large, relatively slow-moving ships.

In both World War I and World War II, similar vulnerability was regularly demonstrated. In World War I, German submarines easily sunk many ships with their torpedoes. In World War II, submarines and their torpedoes again took a heavy toll, but aircraft bombing also was very effective.

Modern warships are built with extremely thick steel hulls, to make them more resistant to such attacks. However, rocket based weapons are MUCH more sophisticated, as well. The example of the single Exocet missile seems clear. That one small missile disabled the ship. What would have happened if 40 such missiles has been launched at that ship? Or at a convoy of ships? Or at a battle fleet? The extremely rapid movement of the rockets and the rather slow movement of the massive ships makes them rather like sitting ducks!

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Many modern foreign rocket-based weapons are radar guided. There may be a way to mislead enemy radars as to the existence and location of ships in a fleet. In 1990, I met with several representatives of the US Government (in Indianapolis) to present and offer this technology. After my presentation, they indicated that they did not feel that there was any actual need for my technology. They also implied that there was nothing particularly secret about what I proposed, so I figured I'd now create this web-page to present it. I am still convinced that the technology has potential value.

Current Stealth Technology

Reflection of ANY radiation (light, radio, radar, etc) occurs in two ways, specular and diffuse. Specular reflection is the extremely identifiable reflection, as when light reflects from a quality mirror. Diffuse reflection is rather different, as when light reflects off a brushed aluminum surface. Radar only works when it receives a reflection of a signal that it sends out. Either kind of reflection can create the echo necessary for radar to work well.

Some American aircraft apply some aspects of Stealth technology. Very angular shapes is quite important in dealing with specular reflections. Think of seeing a car with a curved chrome bumper on a sunny day. This kind of surface creates almost entirely specular reflection. No matter where you are, you see a tiny but very bright reflection of the sun which gets to you. Now, imagine if that bumper didn't have that continuously curved surface, but rather just flat surfaces with sharp edged corners. Now, nearly anywhere you are, you will not see ANY reflection of the sun off of it! It turns out that the boxy shape tends to make ALL the reflection go to one very specific direction, with almost no specular reflection going anywhere else. You may have noticed some flat truck windshields that almost blind you with the reflection, but only when you are at a very specific position.

As applied to radar, as long as the specular reflection is all reflected in ANY OTHER DIRECTION than back to the originating radar station, no specular echo will ever be received, and so the object will be essentially invisible on radar. I had a big, old, ugly, 1972 Ford Van, that I considered modifying as an experiment around 1984. On the front of it, I considered mounting a giant flat (specularly-reflective) metal mirror, with the lower edge farther forward than the top. So it would have sort of looked like a sloped-back wedge from the front! This would have specularly reflected ALL radar signals upward into space, with NONE ever being reflected back to a radar gun. This would have made the big vehicle effectively invisible on Police Radar! (Essentially, only exposed surfaces such as the tires could still reflect radar signals back to a radar gun, but that reflection would be very minimal, comparable to the radar echo off of a dog-sized object. Most radar guns have a sensitivity adjustment where such weak echoes are ignored.)

Of course, as soon as the mirror got even a little dirty, it would then ALSO create DIFFUSE reflection, which WOULD cause a relatively weak echo to get back to an originating Police Radar, so the premise is impractical there. American stealth aircraft have angular shapes for the exact same reason as described above. They deal with minimizing diffuse reflections by using special coatings (paint) to absorb rather than reflecting those wavelengths. By combining the two types of technologies, those aircraft suppress both specular and diffuse reflection, and therefore accomplish virtual invisibility on enemy radars.

Ships

I present all this to show that these technologies have little value for something as large and slow as a ship. There just are no coating materials that exist that have such low reflectivity to make such large objects not reflect enough diffuse radiation to give a radar echo. There might be some value in building ships with angular shapes to reduce specular reflection, but there just is no possible way to keep diffuse reflection from allowing identification of its position. Therefore, a new and different approach is necessary for ships.

The Ship Stealth Invention

Ships operate in an environment of effectively two dimensions, where aircraft operate in three dimensions. This is an advantage that is important in this invention. Nearly any (distant) radar system that would be trying to locate the ship would be on or near the surface of the ocean.

It is briefly necessary now to discuss an entirely different subject. There are some industrial sound-protection safety earmuffs, that are high-tech. Instead of just trying to muffle sounds that approach a person's ears, these products have a microphone to sample the incoming sounds. They then appropriately amplify AND INVERT the signals. It might first seem that the user would then be subjected to TWICE the loudness of the incoming sounds, but that is not true. By precise synchronization of the artificially created inverted signal, the result is that the two loud sound sources cancel each other out, eliminating virtually all of the sound! These hearing-protection devices have become quite common in industry, with current prices of a few hundred dollars.

These products are based on a very well established Physics concept called "destructive interference of waves" Two (traveling) wave patterns which are identical and exactly out of phase with each other will cancel each other out, leaving nothing remaining!

The proposed Ship Stealth invention is based on the same concept. Instead of sound waves, we would be dealing with radar waves, which are equally subject to being cancelled out by the addition of an inverted duplicate signal. The main difference is that sound waves travel relatively slowly (at the speed of sound) while radar waves travel about a million times faster, at the speed of light. Other than that, the situations are quite similar.

Actual Applications

Along the perimeter of the deck of the ship, many receiving antennas would be mounted, on booms mounted outward. They would each be sensing for incoming radar beams. Each would briefly store an electronic copy of that signal. By comparing the timing of reception of such signals from several of these antennas, it is possible to very accurately identify the direction of the source of the radar beam. Previously recorded echo contour signals (say 360 of them, for each degree of azimuth) would be available in a fast computer, that represent the appearance of THAT PARTICULAR ship from each of those specific directions. By now knowing the direction of the originating radar transmitter, the correct echo contour pattern is selected. It is then synchronized with the incoming signal such that it will represent an exact inverted version of the echo that will shortly be produced by the actual echoes off the ship structures. Amplitude of the artificial added inverted signal is also adjusted to match the shape of the envelope of the incoming signal.

The result of this is an almost complete cancellation of the echo from the actual ship structure! The radar installation that sent out the radar beam would NOT receive an echo with which it could become aware of the ship's presence!


An even more advantageous system would seem to be possible, where the actual incoming signal was processed and inverted, and adjusted, as with the sound-protection system mentioned above. Unfortunately, that may not be possible. All this would have to be done in an extremely short period of time, measured in small numbers of nanoseconds. Even with extremely fast computers, actual complete processing of such a signal seems unlikely. This is why I propose using previously recorded copies of the ship's radar echoes, to allow the process to occur rapidly enough.

If the extended boom antennas (possibly with the electronics immediately there, for faster processing) extended out 20 feet beyond the ship body, then around 20 nanoseconds would occur before the incoming radar signal actually hit the ship body, and another 20 nanoseconds would pass while the radar echo traveled back to where the antenna was. At that time, the artificial (inverted) radar echo should begin to be emitted, to cancel out that echo.

For any real computer, with real circuit wires and antenna, this rapid of a response may not be possible. Signals cannot move in wires any faster than the radar signals and echoes move through the air. The computer processing time would almost certainly make it so that at least the first small part of the radar echo would not be able to be cancelled and so it would actually be reflected back to the radar installation. However, as long as the bulk of the echo was nulled out, the received echo would appear to be the echo from a very small boat, rather than from a large ship.


In addition to this last consideration, I suggest an addition to the whole system. Each ship would have a number of unmanned, lifeboat-sized, motorized small boats, which would each have remote radio controls and also a simpler version of the artificial echo electronics. The crew would deploy several dozen of these tiny, unmanned boats, at a considerable distance from the mother ship, and then turn on their artificial echo creators (after first becoming aware of an imminent danger). The resulting display on the source radar screen would be what appeared to be dozens of massive ships and one small boat. If (radar-guided) enemy missiles were then launched, it would not be necessary to try to intercept them, because those missiles would be targeting the stronger artificial radar echoes coming from the unmanned small boats. The ship, which would appear on radar as the small boat, should therefore be quite safe!


I first experimented with what would later be publicly called Stealth technology in 1983 and 1984, during a time when military stealth research was still absolutely secret. (It was not disclosed until around 1988, and more completely around 1990.) I first invented this Ship Stealth shortly after the Exocet missile attack around 1990 that killed American Sailors. This presentation was first placed on the Internet in July 1999.

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C Johnson, Theoretical Physicist, Physics Degree from Univ of Chicago