Stealth Technology for Huge Ocean-Going Ships
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.
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.
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!
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.
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.
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