Editing Submarine (section)

====Snorkel====
{{Main|Submarine snorkel}}
[[File:Submarine snorkel, 1942, the first used by the Swedish Navy, used on Neptun and later Nacken - Marinmuseum, Karlskrona, Sweden - DSC08950.JPG|thumb|right|Head of the snorkel mast from German [[type XXI submarine]] [[German submarine U-3503|''U-3503'']], scuttled outside [[Gothenburg]] on 8 May 1945 but raised by the Swedish Navy and carefully studied for the purpose of improving future Swedish submarine designs]]

During World War II the Germans experimented with the idea of the ''schnorchel'' (snorkel) from captured Dutch submarines but did not see the need for them until rather late in the war. The ''schnorchel'' is a retractable pipe that supplies air to the diesel engines while submerged at [[periscope depth]], allowing the boat to cruise and recharge its batteries while maintaining a degree of stealth.

Especially as first implemented however, it turned out to be far from a perfect solution. There were problems with the device's valve sticking shut or closing as it dunked in rough weather. Since the system used the entire pressure hull as a buffer, the diesels would instantaneously suck huge volumes of air from the boat's compartments, and the crew often suffered painful ear injuries. Speed was limited to {{convert|8|kn|km/h}}, lest the device snap from stress. The ''schnorchel'' also created noise that made the boat easier to detect with sonar, yet more difficult for the on-board sonar to detect signals from other vessels. Finally, allied radar eventually became sufficiently advanced that the ''schnorchel'' mast could be detected beyond visual range.<ref>{{cite book |last=Ireland |first=Bernard |title=Battle of the Atlantic |publisher=Pen & Sword Books |year=2003 |location=Barnsley, UK |page=187 |isbn=978-1-84415-001-4}}</ref>

While the snorkel renders a submarine far less detectable, it is thus not perfect. In clear weather, diesel exhausts can be seen on the surface to a distance of about three miles,<ref>{{cite book|last1=Schull|first1=Joseph|title=The Far Distant Ships|date=1961|publisher=Queen's Printer, Canada|location=Ottawa|pages=259}}</ref> while "periscope feather" (the wave created by the snorkel or periscope moving through the water) is visible from far off in calm sea conditions. Modern radar is also capable of detecting a snorkel in calm sea conditions.<ref>{{cite book|last1=Lamb|first1=James B.|title=On the triangle run|date=1987|publisher=Totem Books|location=Toronto|isbn=978-0-00-217909-6|pages=[https://archive.org/details/ontrianglerun0000lamb/page/25 25, 26]|url=https://archive.org/details/ontrianglerun0000lamb/page/25}}</ref>

[[File:U-3008 Turm.jpg|thumb|right|[[German submarine U-3008|USS ''U-3008'']] (former German submarine ''U-3008'') with her snorkel masts raised at Portsmouth Naval Shipyard, Kittery, Maine]]
The problem of the diesels causing a vacuum in the submarine when the head valve is submerged still exists in later model diesel submarines but is mitigated by high-vacuum cut-off sensors that shut down the engines when the vacuum in the ship reaches a pre-set point. Modern snorkel induction masts have a fail-safe design using [[compressed air]], controlled by a simple electrical circuit, to hold the "head valve" open against the pull of a powerful spring. Seawater washing over the mast shorts out exposed electrodes on top, breaking the control, and shutting the "head valve" while it is submerged. US submarines did not adopt the use of snorkels until after WWII.<ref>{{Cite book|url=https://books.google.com/books?id=GLy8quRc-YYC&q=submarine+snorkel&pg=PA86|title=The Submarine|last=Navy|first=United States|date=September 2008|publisher=United States Printing Office|isbn=978-1-935327-44-8|language=en}}</ref>