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World War Two radar
RADAR (Radio Detection And Ranging) is a technology invented in the
1930s to detect distant objects, mostly aircraft and ships. Since
detection is done by receiving radio waves reflected from the target,
radar works the same by day and night and in all weather, which makes it a
revolutionary long range observation tool, both military, and after world
war 2, also civilian.
World war 2 radar technology
Radar works essentially in the same way that a bat uses sound to 'see'
in total darkness. The radar transmitter produces strong (kilowatts) and
extremely short (about a millionth of a second) pulses of radio energy.
The pulses are transmitted thru the air to a known direction by a
directional antenna. When pulses hit an object, such as an aircraft, a
ship, or the ground, they are reflected by it. The reflections are
received by the radar antenna, and converted by a receiver to an electric
signal that can be displayed to the operator. Since the speed of the
signal is the speed of light, the time between the transmission and the
reception of a pulse indicates the distance of the target, and together
with knowing the direction at which the antenna transmits, the position of
the detected target is known.
Initially radars were equipped with display devices like those in an
electronics lab (oscilloscope), but later more operationally useful
devices were invented, particularly the PPI (Plan Position Indicator)
which is the familiar radar display in which a circular display shows a
beam which rotates with the rotating radar antenna, and marks with light
the positions of detected targets relative to their range.
Electronically, PPI works basically like the lab oscilloscope display,
but because of the rotation it creates a map-like display that the
operator understands intuitively and immediately, as if he was looking at
a map where the radar's own position is in the centre, and the map
position of detected targets are marked with small dots of light. The
operational advantage of this display method was enormous, because it
eliminated the need to calculate and check directions on a map. PPI is the
map that shows the operator clearly where the targets are.
From military point of view there are basically two types of radar,
used for detection and for fire control.
Detection radars are used to create a radar map of all objects in all
directions and often as far as possible. They are mostly used for purposes
such as early warning detection of aircraft and ships, ground
controlled intercept of aircraft, which is done by directing fighter
aircraft to detected incoming aircraft, and mapping of the ground
terrain for navigation and targeting, mostly by bombers.
Fire control radars are the radar equivalent of a searchlight. They are
dedicated to the precise positioning of a previously detected particular
target, precise enough to aim guns at it and hit it without actually
seeing it, or at least to guide the operator so close to it that it
finally can be seen, even if only as a dark shadow, and then to aim guns
at it and hit it. Fire control radars were used mostly by night fighters,
which were usually twin engine aircraft, larger than day fighters, which
could carry not just the pilot but also a heavy radar, a radar operator,
and were heavily armed in order to make sure that the target, a heavy
bomber, will be destroyed by the first burst of their guns, because unlike
day fighter pilots which could pursuit their target, night fighter pilots
could 'see' only the narrow cone ahead of them that was 'lit' by their
radar, and unless the target was destroyed, its pilot could immediately
break away into a deep dive or other evasive manoeuvres and unless it was
burning it could quickly disappear in the darkness.
An interesting combination of using a radar and a searchlight for fire
control was used in anti-submarine aircraft which hunted German submarines
in the Atlantic. After a surfaced submarine, or even just the periscope of
a submerged submarine, was detected by radar, the radar operator guided
the pilot to it, but since it was such a small target, and one that had to
be precisely hit in the 1st attempt or it would disappear, and since
radars can't detect below a certain minimum range, the aircraft pilot just
had to see the target with his eyes in order to direct the aircraft right
over it and drop the depth charges at the right moment. To be able to do
so at night, these bombers carried a powerful fixed searchlight aimed
forward, and it was lit in the last few seconds. Early enough for the
pilot to actually see the target on the water ahead of him, and too late
for the submarine to dive.
Electronic Warfare and Electronic Intelligence
The greatest advantage of using radar is that it denies the enemy of
the ability to use the element of surprise, of being hidden by distance,
by night or by clouds until it's too late to defend against it or to
attack it before it disappears. The response was obvious, the side that
wanted to avoid being detected by radar wanted to know if and where it was
being detected by radar, and also to be able to neutralize enemy radar in
order to regain the element of surprise. This started a dramatic and
secret electronic arms race between radar developers and those who develop
measures against radar, an arms race which continues since world war 2.
The first development was radar detectors. The basic types, carried
mostly by bombers and submarines, could tell their operators if a radar
was transmitting at them (and therefore could detect them) and could
estimate if it was near or distant, by the power of the radar waves. The
more advanced radar detectors were used to analyze everything possible
about enemy radars, their power, radio wave frequency, pulse rate, pulse
width, and other technical parameters from which engineers could learn a
lot about the capabilities of enemy radars, and design 'electronic
warfare' counter-measures to use against them.
They could also help determine where enemy radars were positioned, so
they could be attacked, or bypassed, or in one special case, stolen! - in
late 1941, British intelligence noticed that one German early warning
radar position, in Bruneval, Belgium, was positioned very close to the
beach. It was on a cliff, but not far from a path going down to the water.
This was enough for British commandos to raid the isolated German radar
station in Bruneval one winter night in 1942, dismantle the radar, with
the help of a radar specialist who came with them, and take it all back to
England in a motor boat, for a complete analysis of this particular type
and of German radar technology in general. (this bold idea was repeated in
1969 when Israeli commandos dismantled and lifted a radar in Egypt with
helicopters)
Once much is known about enemy radars, they can either be attacked, if
they're in range for a precision attack by dive bombers or
fighter-bombers, or more commonly they can be disrupted by electronic
warfare, which in world war 2 included two main types of counter-measures:
jammers transmit strong radio waves in the same frequency as the
radar, which saturate the radar receiver with signals so much that it
can't see the weaker signals of real targets. chaff (nicknamed
'window' by the royal air force) are a cloud of thin lightweight strips of
metal cut to a specific size, which can be dispersed from a heavy bomber.
These strips are designed to be detected by radar and therefore instead of
detecting isolated real targets, the radar operator sees just a huge
cloud. There are various ways for radar operators and designers to
partially counter these counter-measures, partly by having highly trained
and experienced operators, partly by technological solutions, and partly
by direct action, using radar detectors on night fighters to locate and
destroy the jammer-carrying aircraft.
Notable world war 2 radar types
Funkmessgerät Typ. Freya - with two antenna systems, one for horizontal
and one for vertical use
Freya fitted to a German night fighter
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Wurzburg - a German GCI (Ground Controlled Intercept) radar used to
direct fighters, especially night fighters, close enough to enemy
bombers that their pilots could then independently intercept them,
visually at day, or by radar at night (range: 18 miles)
Würzburg-Riese radar
Lichtenstein BC fitted to a Ju 88
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Chain Home - a network of British early warning radars used to
defend Britain in the Battle Of Britain. It was an early and primitive
radar, but it was powerful and reliable, and was efficiently operated by
experienced operators, and therefore was a critical asset which allowed
the British Fighter Command to optimally engage incoming German bomber
formations. (range: 185 miles)
Chain Home radar masts
ASV (Aircraft to Surface Vessel) radar was tested in Avro Ansons
H2S radar plot |
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