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A periscope is an instrument for observation over, around or through an object, obstacle or condition that prevents direct line-of-sight observation from an observer's current position. In its simplest form, it consists of an outer case with mirrors at each end set parallel to each other at a 45° angle. This form of periscope, with the addition of two simple lenses, served for observation purposes in the trenches during World War I. Military personnel also use periscopes in some gun turrets and in armoured vehicles. More complex periscopes using prisms or advanced
fiber optics An optical fiber, or optical fibre in Commonwealth English, is a flexible, transparent fiber made by drawing glass (silica) or plastic to a diameter slightly thicker than that of a human hair. Optical fibers are used most often as a means to ...
instead of mirrors and providing magnification operate on
submarine A submarine (or sub) is a watercraft capable of independent operation underwater. It differs from a submersible, which has more limited underwater capability. The term is also sometimes used historically or colloquially to refer to remotely op ...
s and in various fields of science. 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

Johannes Hevelius described an early periscope (which he called a "polemoscope") with lenses in 1647 in his work ''
Selenographia, sive Lunae descriptio ''Selenographia, sive Lunae descriptio'' (''Selenography, or A Description of The Moon'') was printed in 1647 and is a milestone work by Johannes Hevelius. It includes the first detailed map of the moon, created from Hevelius's personal observat ...
'' elenography, or an account of the Moon Hevelius saw military applications for his invention. In 1854,
Hippolyte Marié-Davy Edme Hippolyte Marié-Davy (28 April 1820 – 26 July 1893) was a French chemist and inventor during the 19th century. He was born in Clamecy, Nièvre. In 1854, he invented the first naval periscope, consisting in a vertical tube with two smal ...
invented the first naval periscope, consisting of a vertical tube with two small mirrors fixed at each end at 45°. Simon Lake used periscopes in his submarines in 1902. Sir Howard Grubb perfected the device in World War I.
Morgan Robertson Morgan Andrew Robertson (September 30, 1861 – March 24, 1915) was an American author of short stories and novels, and the self-proclaimed inventor of the periscope. Early life Robertson was the son of Andrew Robertson, a ship captain on the ...
(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, served in World War I (1914–1918) to enable soldiers to see over the tops of trenches, thus avoiding exposure to enemy fire (especially from snipers).Willmott, H.P. (2003) ''First World War''. Dorling Kindersley. p. 111. The
periscope rifle A periscope rifle is a rifle that has been adapted to enable it to be sighted by the use of a periscope. This enables the shooter to remain concealed below cover. The device was independently invented by a number of individuals in response to the t ...
also saw use during the war – this was an infantry rifle sighted by means of a periscope, so the shooter could aim fire the weapon from a safe position below the trench parapet. During World War II (1939–1945), artillery observers and officers used specifically-manufactured periscope binoculars with different mountings. Some of them also allowed estimating the distance to a target, as they were designed as stereoscopic rangefinders.


Armored vehicle periscopes

Tanks and armoured vehicles use periscopes: they enable drivers, tank commanders, and other vehicle occupants to inspect their situation through the vehicle roof. Prior to periscopes, direct vision slits were cut in the armour for occupants to see out. Periscopes permit view outside of the vehicle without needing to cut these weaker vision openings in the front and side armour, better protecting the vehicle and occupants. A protectoscope is a related periscopic vision device designed to provide a window in armoured plate, similar to a direct vision slit. A compact periscope inside the protectoscope allows the vision slit to be blanked off with spaced armoured plate. This prevents a potential ingress point for small arms fire, with only a small difference in vision height, but still requires the armour to be cut. In the context of armoured fighting vehicles, such as tanks, a periscopic vision device may also be referred to as an
episcope Episcope may refer to: *An opaque projector *The ministry of Oversight within various Christian Churches and in ecumenical dialogue. *An indirect vision device similar to a periscope used in armoured fighting vehicle An armoured fighting vehi ...
. In this context a periscope refers to a device that can rotate to provide a wider field of view (or is fixed into an assembly that can), while an episcope is fixed into position. Periscopes may also be referred to by slang, e.g. "shufti-scope".


Gundlach and Vickers 360-degree periscopes

An important development, the Gundlach rotary periscope, incorporated a rotating top with a selectable additional prism which reversed the view. This allowed a tank commander to obtain a 360-degree field of view without moving his seat, including rear vision by engaging the extra prism. This design, patented by Rudolf Gundlach in 1936, first saw use in the
Polish Polish may refer to: * Anything from or related to Poland, a country in Europe * Polish language * Poles, people from Poland or of Polish descent * Polish chicken *Polish brothers (Mark Polish and Michael Polish, born 1970), American twin screenwr ...
7-TP The 7TP (''siedmiotonowy polski'' - 7-tonne Polish) was a Polish light tank of the Second World War. It was developed from the British Vickers 6-ton. A standard tank of the Polish Army during the 1939 Invasion of Poland, its production did not ...
light tank (produced from 1935 to 1939). As a part of Polish–British pre- World War II military cooperation, the patent was sold to Vickers-Armstrong where it saw further development for use in British tanks, including the Crusader,
Churchill Sir Winston Leonard Spencer Churchill (30 November 187424 January 1965) was a British statesman, soldier, and writer who served as Prime Minister of the United Kingdom twice, from 1940 to 1945 during the Second World War, and again from 1 ...
,
Valentine A valentine is a card or gift given on Valentine's Day, or one's sweetheart. Valentine or Valentines may also refer to: People and fictional characters * Valentine (name), a given name and a surname, including a list of people and fictional char ...
, and ''
Cromwell Oliver Cromwell (25 April 15993 September 1658) was an English politician and military officer who is widely regarded as one of the most important statesmen in English history. He came to prominence during the 1639 to 1651 Wars of the Three Ki ...
'' models as the
Vickers Tank Periscope MK.IV The Gundlach Periscope, usually known under its British designation as Vickers Tank Periscope MK.IV, was a revolutionary invention by Polish engineer Rudolf Gundlach, manufactured for Polish 7TP tanks from the end of 1935 and patented in 1936 as ...
. The Gundlach-Vickers technology was shared with the
American Army The United States Army (USA) is the land service branch of the United States Armed Forces. It is one of the eight U.S. uniformed services, and is designated as the Army of the United States in the U.S. Constitution.Article II, section 2, cla ...
for use in its tanks including the
Sherman Sherman most commonly refers to: *Sherman (name), a surname and given name (and list of persons with the name) ** William Tecumseh Sherman (1820–1891), American Civil War General *M4 Sherman, a tank Sherman may also refer to: Places United St ...
, built to meet joint British and US requirements. This saw post-war controversy through legal action: "After the Second World War and a long court battle, in 1947 he, Rudolf Gundlach, received a large payment for his periscope patent from some of its producers." The USSR also copied the design and used it extensively in its tanks, including the T-34 and T-70. The copies were based on Lend-Lease British vehicles, and many parts remain interchangeable. Germany also made and used copies.Łukomski, Grzegorz and Stolarski, Rafał E. (1999) ''Nie tylko Enigma... Mjr Rudolf Gundlach (1892–1957) i jego wynalazek'' (Not Only Enigma... Major Rudolf Gundlach (1892–1957) and His Invention), Warsaw-London.


Periscopic gun-sights

Periscopic
sights A sight is an aiming device used to assist in visually aligning ranged weapons, surveying instruments or optical illumination equipments with the intended target. Sights can be a simple set or system of physical markers that have to be aligne ...
were also introduced during the Second World War. In British use, the Vickers periscope was provided with sighting lines, enabling front and rear prisms to be directly aligned to gain an accurate direction. On later tanks such as the Churchill and Cromwell, a similarly marked episcope provided a backup sighting mechanism aligned with a vane sight on the turret roof. Later, US-built Sherman tanks and British
Centurion A centurion (; la, centurio , . la, centuriones, label=none; grc-gre, κεντυρίων, kentyríōn, or ) was a position in the Roman army during classical antiquity, nominally the commander of a century (), a military unit of around 80 ...
and Charioteer tanks replaced the main telescopic sight with a true periscopic sight in the primary role. The periscopic sight was linked to the gun itself, allowing elevation to be captured (rotation being fixed as part of rotating turret). The sights formed part of the overall periscope, providing the gunner with greater overall vision than previously possible with the telescopic sight.


Modern specialised AFV periscopes

In modern use, specialised periscopes can also provide night vision. The Embedded Image Periscope (EIP) designed and patented by Kent Periscopes provides standard unity vision periscope functionality for normal daytime viewing of the vehicle surroundings plus the ability to display digital images from a range of on-vehicle sensors and cameras (including thermal and low light) such that the resulting image appears "embedded" internally within the unit and projected at a comfortable viewing positions.


Naval use

Periscopes allow a
submarine A submarine (or sub) is a watercraft capable of independent operation underwater. It differs from a submersible, which has more limited underwater capability. The term is also sometimes used historically or colloquially to refer to remotely op ...
, when submerged at a relatively shallow depth, to search visually for nearby targets and threats on the surface of the water and in the air. When not in use, a submarine's periscope retracts into the
hull Hull may refer to: Structures * Chassis, of an armored fighting vehicle * Fuselage, of an aircraft * Hull (botany), the outer covering of seeds * Hull (watercraft), the body or frame of a ship * Submarine hull Mathematics * Affine hull, in affi ...
. A submarine commander in tactical conditions must exercise discretion when using his periscope, since it creates a visible wake (and may also become detectable by radar), giving away the submarine's position. Marie-Davey built a simple, fixed naval periscope using mirrors in 1854. Thomas H. Doughty of the United States Navy later invented a prismatic version for use in the American Civil War of 1861–1865. Submarines adopted periscopes early. Captain Arthur Krebs adapted two on the experimental French submarine in 1888 and 1889. The Spanish inventor Isaac Peral equipped his submarine (developed in 1886 but launched on September 8, 1888) with a fixed, non-retractable periscope that used a combination of prisms to relay the image to the submariner. (Peral also developed a primitive
gyroscope A gyroscope (from Ancient Greek γῦρος ''gŷros'', "round" and σκοπέω ''skopéō'', "to look") is a device used for measuring or maintaining orientation and angular velocity. It is a spinning wheel or disc in which the axis of rota ...
for submarine navigation and pioneered the ability to fire live torpedoes while submerged.) The invention of the collapsible periscope for use in submarine warfare is usually credited to Simon Lake in 1902. Lake called his device the "omniscope" or "skalomniscope". modern submarine periscopes incorporate lenses for magnification and function as telescopes. They typically employ prisms and total internal reflection instead of mirrors, because prisms, which do not require coatings on the reflecting surface, are much more rugged than mirrors. They may have additional optical capabilities such as
range-finding A rangefinder (also rangefinding telemeter, depending on the context) is a device used to measure distances to remote objects. Originally optical devices used in surveying, they soon found applications in other fields, such as photography a ...
and targeting. The mechanical systems of submarine periscopes typically use hydraulics and need to be quite sturdy to withstand the drag through water. The periscope chassis may also support a radio or radar antenna. Submarines traditionally had two periscopes; a navigation or observation periscope and a targeting, or commander's, periscope. Navies originally mounted these periscopes in the
conning tower A conning tower is a raised platform on a ship or submarine, often armored, from which an officer in charge can conn the vessel, controlling movements of the ship by giving orders to those responsible for the ship's engine, rudder, lines, and gro ...
, 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, used to scan the sea surface and sky, 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. 21st-century submarines do not necessarily have periscopes. The United States Navy's s and the Royal Navy's s instead use
photonics mast A photonics mast (or '' optronics mast''BBC News Scotland, A vision of evolving technologies' 30 August 2007, 13:06 GMT) is a sensor on a submarine which functions similarly to a periscope without requiring a periscope tube, thus freeing design ...
s, pioneered by the Royal Navy's , 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 in placing internal equipment.


See also

* Coincidence rangefinder *
Relay lens In optics, a relay lens is a lens or a group of lenses that receives the image from the objective lens and relays it to the eyepiece. Relay lenses are found in refracting telescopes, endoscopes, and periscopes to optically manipulate the light ...
* Rangefinder *
Vickers Tank Periscope MK.IV The Gundlach Periscope, usually known under its British designation as Vickers Tank Periscope MK.IV, was a revolutionary invention by Polish engineer Rudolf Gundlach, manufactured for Polish 7TP tanks from the end of 1935 and patented in 1936 as ...


References


External links


''The Fleet Type Submarine Online: Submarine Periscope Manual''
United States Navy Navpers 16165, June 1979
''Simulation of a Periscope''
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NTNUJAVA Virtual Physics Laboratory
{{Authority control Optical devices British inventions 1902 introductions Submarine components