Editing Periscope (section)

==Naval use==
[[File:1889 Arthur Krebs & Jean Rey periscope for the french Gymnote submarine.jpg|thumb|1889 Arthur Krebs & Jean Rey periscope for the French submarine ''Gymnote'']]
Periscopes allow a [[submarine]], 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 (watercraft)|hull]]. 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]]),<ref>{{Cite web|url=http://www.navy.mil/navydata/fact_display.asp?cid=2100&tid=1300&ct=2|title=The US Navy – Fact File: AN/SPS-74(V) Radar Set|last=Petty|first=Dan|website=www.navy.mil|language=en|access-date=2017-11-29|archive-date=2019-02-14|archive-url=https://web.archive.org/web/20190214061316/https://www.navy.mil/navydata/fact_display.asp?cid=2100&tid=1300&ct=2|url-status=dead}}</ref><ref>{{Cite journal|last1=Ousborne|first1=Jeffrey|last2=Griffith|first2=Dale|last3=Yuan|first3=Rebecca W.|date=1997|title=A Periscope Detection Radar|url=http://techdigest.jhuapl.edu/TD/td1801/ousbourn.pdf|journal=Johns Hopkins APL Technical Digest|volume=18|pages=125|access-date=2017-11-29|archive-date=2017-08-08|archive-url=https://web.archive.org/web/20170808171500/http://techdigest.jhuapl.edu/TD/td1801/ousbourn.pdf|url-status=dead}}</ref> 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 {{ship|French submarine|Gymnote|Q1|2}} in 1888 and 1889. The Spanish inventor [[Isaac Peral]] equipped his submarine {{ship|Spanish submarine|Peral||2}} (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]] for submarine navigation and pioneered the ability to fire live [[torpedo]]es while submerged.<ref>{{Cite web |url=http://pedrocurto.com/1.html |title=El Arma Submarina Española |access-date=2009-10-21 |archive-date=2009-12-17 |archive-url=https://web.archive.org/web/20091217120312/http://pedrocurto.com/1.html |url-status=dead }}</ref>{{Unreliable source?|date=March 2011}})

The invention of the collapsible periscope for use in submarine warfare is usually credited{{By whom|date=January 2010}} to [[Simon Lake]] in 1902. Lake called his device the "omniscope" or "skalomniscope".{{Citation needed|date=January 2010}}

{{As of|2009}} modern submarine periscopes incorporate lenses for magnification and function as [[telescope]]s. They typically employ [[Prism (optics)|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|range-finding]] and targeting. The mechanical systems of submarine periscopes typically use [[Hydraulic machinery|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]], one forward of the other in the narrow hulls of diesel-electric submarines. In the much wider hulls of {{as of | 2009 | alt = recent}} [[United States Navy|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 acoustic "ping" that gave away the location of the submarine) and most torpedoes were unguided.

Twenty-first-century submarines do not necessarily have periscopes.  The United States Navy's {{sclass|Virginia|submarine|1}}s and the [[Royal Navy]]'s {{sclass|Astute|submarine|1}}s instead use [[photonics mast]]s,<ref name="Publishing2011">{{cite book|title=War at Sea and in the Air|url=https://books.google.com/books?id=TfOcAAAAQBAJ&pg=PA65|date=1 November 2011|publisher=Britannica Educational Publishing|isbn=978-1-61530-753-1|page=65}}</ref> pioneered by the Royal Navy's {{HMS|Trenchant|S91|6}}, 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.

{{Gallery
|title=Naval use
|align=center
|File:Submarine periscope.jpg|Officer at periscope in control room of a U.S. Navy submarine in World War II
|File:Attack periscope.png|Submarine monocular attack periscope
|File:Torpedoed Japanese destroyer Yamakaze sinking on 25 June 1942.jpg|Torpedoed Japanese destroyer {{ship|Japanese destroyer|Yamakaze|1936|2}} photographed through periscope of {{USS|Nautilus|SS-168|6}}, 25 June 1942.
}}