A
periscope is an instrument for observation from
a concealed position. In its simplest form, it is a tube in each
end of which are
mirrors set parallel to each
other at 45 degree angle.
This form of periscope, with the addition of two simple lenses,
served for observation purposes in the trenches during
World War I. Periscopes are also used in some
gun turrets and
armored vehicles.
More complex periscopes, using
prism
instead of mirrors, and providing magnification, are used on
submarines. The overall design of the
classical submarine periscope is very simple: two telescopes
pointed into each other. If the two telescopes have different
individual magnification, the difference between them causes an
overall magnification or reduction.
Early examples

British trench periscope, Cape Helles
1915
Johann Gutenberg, better known for his
contribution to printing technology,
marketed a periscope in the 1430s to enable pilgrims to see over
the heads of the crowd at the vigintennial religious festival at
Aachen
. Simon Lake used
periscopes in his submarines in 1902.
Sir
Howard Grubb perfected the device in World War I.
Morgan Robertson (1861-1915) claimed to
have tried to patent the periscope: he described a submarine using
a periscope in his fictional works.
Periscopes, in some cases fixed to
rifles, were used in
World War I to enable soldiers to see over of
the tops of trenches, so that they would not be exposed to enemy
fire (especially from snipers).
Periscopes are extensively used in
tanks,
enabling drivers or tank's commanders to inspect the situation
without leaving the safety of the tank. An important development,
Gundlach's periscope, had a rotating
top, allowing a tank commander to obtain 360 degree view without
moving.The design was first used in the
Polish 7-TP light tank.
Shortly before the war it was given to the
British and was used in most tanks of
WWII, including the British
Crusader,
Churchill,
Valentine, and
Cromwell and the
American Sherman. The design was later copied and
used extensively in tanks of the
USSR
(including the
T-34 and
T-70) and
Germany.Periscopes
proved useful in
trench warfare, as
seen in the illustrations, representative of action at
Gallipoli.
Naval use
Periscopes allow a submarine, submerged at a shallow depth, to
search for targets and threats in the surrounding sea and air. When
not in use, the periscope is retracted into the hull. A submarine
commander in tactical conditions must exercise discretion when
using his periscope, since it creates an observable wake and may be
detectable to radar, giving away the sub's position.
A simple, fixed naval periscope using mirrors was built by the
Frenchman Marie Davey in 1854. Thomas H. Doughty of the US Navy
later invented a prismatic version for use in the
American Civil War (1861-1865).
The invention of the collapsible periscope for use in submarine
warfare is usually credited to
Simon Lake
in 1902, who called his device the
omniscope or
skalomniscope. There is also a report that an Italian,
Triulzi, demonstrated such a device in 1901 calling it a
cleptoscope.
In another early example of naval use of periscopes, Captain
Arthur Krebs adapted two on the
experimental French submarine
Gymnote in 1888 and 1889. Perhaps the earliest
example comes from the Spanish inventor Isaac Peral on his
submarine in 1888
Peral - developed
in 1886 but launched on September 8, 1888. Peral's fixed,
non-retractable periscope used a combination of prisms to rely the
image to the submariner, but his submarine pioeneered the ability
to fire live torpedoes while submerged. Peral also developed a
primitive gyroscope for his submarine navigation.

A torpedoed Japanese destroyer,
photographed through periscope of U.S.S.
A modern submarine periscope incorporates lenses for magnification
and functions as a
telescope. It typically
employs
prism and
total internal reflection instead
of mirrors, because prisms, which do not require coatings on the
reflecting surface, are much more rugged than mirrors. It may have
additional optical capabilities such as
range-finding and targeting. The mechanical
systems of submarine periscopes typically use hydraulic power and
need to be quite sturdy to withstand the drag through water. The
periscope chassis may also be used to support a radio or radar
antenna.
Submarines traditionally had two periscopes: a navigation or
observation periscope and a targeting, or commander's, periscope.
Early navies originally mounted these periscopes in the
conning tower, one forward of the other in the
narrow hulls of diesel-electric submarines. In the much wider hulls
of US Navy submarines, the two operate side-by-side. The
observation scope was used to scan the sea surface and sky and
typically had a wide field of view and no magnification or
low-power magnification. The targeting or "attack" periscope, by
comparison, had a narrower field of view and higher magnification.
In World War II and earlier submarines it was the only means of
gathering target data to accurately fire a
torpedo, since
sonar was not
yet sufficiently advanced for this purpose (ranging with sonar
required emission of an electronic "ping" that gave away the
location of the submarine) and most torpedoes were unguided.
However, 21st century submarines do not necessarily have
periscopes. The
United States
Navy's
Virginia-class submarines
instead use
photonics masts, which
lift an electronic imaging sensor-set above the water. Signals from
the sensor set travel electronically to workstations in the
submarine's control center. While the cables carrying the signal
must penetrate the submarine's hull, they use a much smaller and
more easily sealed—and therefore less expensive and safer—hull
opening than those required by periscopes. Eliminating the
telescoping tube running through the conning tower also allows
greater freedom in designing the pressure hull and placing internal
equipment.
See also
References
External links