To the ancient Greeks it was called the Helm of Hades or the cap of Hades a
special helmet that would make the wearer invisible. In Welsh and Germanic
folklore as well as are all modern-day fictional equivalent of Harry Potter
there is the cloak of invisibility, a magical item that can also make the
wearer invisible so it would only seem right that the military has been striving
to create its own version of invisibility as long as we've had
camouflage but other than painting your face green and brown and wearing grass
on your head, what else has been done to make the military invisible.
Do you remember the film the Philadelphia Experiment well just in
case you haven't seen it it's about a world war two experiment to make a US
Navy destroyer, the USS Eldridge invisible though in the film the field
generator they use makes the ship disappear and move through space and
time and when it comes back strange things have happened at a crew. Well the
basis of the film is actually true to make a ship invisible but not so as you
couldn't see it but invisible magnetically so that it wouldn't trigger
magnetic mines. This technique is known as Degaussing,
effectively demagnetizing after the unit of magnetism called the Gauss. During
World War 2 the Germans used magnetic mines which detected an increase in the
Earth's north magnetic field when a ship passed over it, this was causing havoc
with the British fleet in the North Sea in the English Channel. In 1939 after
recovering a mine accidentally dropped on mudflats at low
tide off of the southeast coast of England, the British were able to work
out how the mines worked and then developed methods to reduce the magnetic
effect. that the ships had. To degauss or demagnetize the biggest ships, giant
coils of wire were fitted around their perimeters on things like aircraft
carriers and troop carriers and several thousand amps passed through them. This
was powered by the ship's generators like a giant electromagnet and he added
a slight south magnetic bias which offset the magnetic effect of a ship
near the mines. This had its limitations as it could only be used on the biggest
ships of enough electrical power to run it and also where in the world it would
be used because the Earth's magnetic field varies in strength in different
locations, it would also need to be reversed if it
were to be used in the southern hemisphere for example. Over time the
mines became more sophisticated so today the latest degaussing systems can match
the magnetic field of a ship to background magnetic field anywhere in
the world effectively making it magnetically invisible. Now whilst this
help protect the ships against mines ships could still be seen by their
biggest threat submarines. During the first world war a technique of painting
large abstract lines shapes and contrasting colors over ships was
developed called dazzle camouflage and the ship's gained the nickname of dazzle
ships or razzle dazzle in the US. Now you may be wondering why you would make a
grey ship in the grey North Atlantic standout with these massive abstract
patterns but these were not to hide the ship these confusing markings were to
make it difficult for submarine commanders to work out the ships type,
heading and speed. From side on they helped disguise the shape by which the ships
could be identified and from oblique angles you can see what it makes it
harder to work out which end is which and thus the ships heading. This was to
try and make the Germans get their torpedo firing positions wrong so they
would miss the ships. In World War one and World War two over six thousand
allied warships used these dazzle patterns with each pattern being
different. The problem was that because everyone was different they couldn't
tell which patterns worked well and which didn't and as World War two
progressed advances using planes and radar made dazzle ships less relevant.
Now the main enemy of a convoy of ships was the u-boats and in World War two
Allied planes were used to find and attack submarines whilst they were still
on the surface but the u-boat crews could often see the planes approaching
by the dark silhouettes against the lighter sky and this gave them time to
dive before the planes could engage. In 1943 the US Navy tried out a technique
which had been developed by the Canadian Navy called diffused lighting camouflage.
The US Navy created project Yehudi this used lights similar to sealed beam car
headlights mounted on the front of the plane
along the leading edges on the wings these were automatically controlled by a
photocell so that the brightness of the lights matched that of the sky behind
the plane this apparently simple idea made the plane blend into the sky by
breaking up the dark silhouette. The idea was refined and in 1945 tests with a
grumman Avenger showed that it was able to get within 2.7 kilometers of the target
ship without being detected whereas without the Yehudi lights it was visible
19 kilometers away. Although these worked well by the time
of the end of the war radar had made the Yehudi light system pretty much
redundant but that didn't mean to say that it was a bad idea,
in fact it's being the basis of many ideas to apparently bend light around an
object to make it appear invisible. The most notable of these is adaptive
camouflage which has only really been possible in recent years with new
electrochromatic materials and flexible OLED displays. The principle is similar
to the Yehudi lights but instead of using a photocell they use a camera on
the opposite side of the vehicle to which it has been seen and this displays the
image of what the camera is seeing onto the watched side so effectively you don't
see the vehicle itself you just see what you would see if it wasn't there.
Now close-up this wouldn't fool anyone but from far away it can help it blend
into the background. Now whilst this might work for visible light most
weapons use infrared or heat to lock on to their target so the latest active
camouflage uses thermo-electric panels. The system called adaptiv by BEA
Systems has about a thousand or so of these small hexagonal panels also known
as Peltier panels which can be heated or cooled by applying an electric current
to them. Infrared cameras pick up the background infrared radiation and
relay this to the Peltier panels to effectively hide the vehicle's infrared
signature from weapons or enemy spotters by matching
background infrared levels. As the sides the vehicle are effectively now one
large infrared display the shape of another object can be projected onto it
like in this example where the silhouette of a tank is made to look
like that of a car it could even flash text messages which would only be seen
in infrared. Now this isn't the full invisibility as we have seen in the
movies but we are getting closer to approximating it although you do have to
say with what we know of current technologies bending light around an
object is going to take some serious science which brings us onto our sponsor
for this video because if you are interested in science then you should
check out brilliant. Brilliant is a problem-solving website that teaches you
to think like a scientist instead of passively listening to lectures you get
to master concepts by solving fun and challenging problems and brilliant
provides the tools and frameworks you need to tackle these challenges
brilliance thought-provoking content is based around breaking up complexities
into bite-sized understandable chunks that will lead you from curiosity to
mastery so what are you waiting for hop on over to brilliant.org/CuriousDroid and sign up for free and the first 200 who do so will get 20%
for the annual premium subscription.