Periscope

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.Australian Light Horse troops using a periscope rifle, Gallipoli, 1915. Photograph by Ernest Brooks.An Auxiliary Periscope for Submarines from The Electrical Experimenter, Vol. IV, No. 38., 1916A team of German artillery observers using periscope binoculars, 1943A First World War periscope made by R & J Beck Ltd in 1918Officer at periscope in control room of a U.S. Navy submarine in World War II. The officer pictured is Captain Raymond W. Alexander, Sr. and the photo was taken in 1942.Submarine monocular attack periscopeTorpedoed Japanese destroyer Yamakaze photographed through periscope of USS Nautilus, 25 June 1942. 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 instead of mirrors and providing magnification operate on submarines 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. Johannes Gutenberg, known for his contribution to printing technology, marketed a kind of periscope in the 1430s to enable pilgrims to see over the heads of the crowd at the vigintennial religious festival at Aachen. Johannes Hevelius described an early periscope with lenses in 1647 in his work Selenographia, sive Lunae descriptio . Hevelius saw military applications for his invention. In 1854, Hippolyte Marié-Davy 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 (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). The periscope rifle 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. 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.