Editing SEAL Delivery Vehicle (section)

==Design==
SDVs carry a pilot, co-pilot, and four person combat swimmer team and their equipment to and from maritime mission objectives on land or at sea. The pilot and co-pilot are often a part of the fighting team. The SDV is [[silver-zinc battery]] powered and equipped with propulsion, navigation, communication, and life-support equipment.<ref name=Museum /> The batteries directly power the electric motor that drives the single screw propeller.<ref name=Museum /> Because they are all electric, SDVs are extremely difficult to detect using passive sonar, and their small size makes them hard to detect using other means.<ref name=Kelly /> The Mark 8 Mod 1 SDV can deliver four fully equipped SEALs to the mission area, be "parked" or loiter in the area, retrieve the SEALs, and then return to the launch site. The SEALs sit upright in the Mark 8, with the pilot and co-pilot/navigator facing forward and the other four facing aft.<ref name=Kelly /> For air, the SEALs rely on their own [[Diving cylinder|air tank]]s or [[rebreather]]s, supplemented by compressed air tanks on the SDV. The crew and passenger compartment in the Mark 8 is small, cramped, and pitch black except for the dim lights of the instrument panel;<ref name=Thompson /> SEALs describe riding in an SDV as like "being locked in a little black coffin deep under the water."<ref name=Kelly /> A 2011 article reported that out of 2,600 SEALS roughly 230 are trained to operate the SDVs. <ref name="Thompson" />

SDVs are generally launched from a [[Dry Deck Shelter]] on the back of a [[submarine]], although they can also be deployed from [[Amphibious assault ship|amphibious carrier]]s and other surface ships equipped to launch and recover the SDV. SDVs are launched and recovered by surface ships using a crane.<ref name=Kelly /> They can also be [[airdrop]]ped (uncrewed) into an operational area from a [[C-130 Hercules]] airplane.<ref name=GS>{{cite web|url=http://www.globalsecurity.org/military/systems/ship/sdv.htm|title=SEAL Delivery Vehicle [SDV]|first=John|last=Pike|website=Global Security |access-date=4 September 2018}}</ref> Finally, the SDV can be launched from the shore.<ref name=Kelly98 />

An SDV can be launched from one platform and recovered by another. {{USS|John Marshall|SSBN-611|6}} demonstrated this capability during a multilateral exercise in the [[Mediterranean]] when it recovered and then launched another country's SDV.<ref name=Kelly98 />

===Mark 8 SDV===
The Mark 8 Mod 1 SDV is the only SDV officially in use by the US Navy and Royal Navy. It is an upgrade of the earlier Mark 8 Mod 0 SDV. The Mod 1 is quieter, faster, more efficient, and has a longer range than the Mod 0.<ref name=Klose /> Its updated electronics, materials, and battery and motor systems gives it twice the range and 1.5 times the speed of the Mod 0.<ref name=Klose>{{cite journal |last1=Klose |first1=John |title=SDV Units in Great Demand as Speed, Range Improve |journal=Seapower |date=July 2003 |url=http://www.navyleague.org/sea_power/jul_03_24.php |access-date=5 September 2018 |archive-date=6 September 2018 |archive-url=https://web.archive.org/web/20180906052703/http://www.navyleague.org/sea_power/jul_03_24.php |url-status=dead }}</ref> Another advantage of the Mark 8 Mod 1 over its predecessor is that it is built from aluminium instead of plastic reinforced fiberglass, making its hull sturdier and roomier.<ref name=Klose /> The sturdier hull means that it can be deployed from [[CH-46 Sea Knight]] and [[CH-53E Super Stallion]] helicopters, although SDVs often break or explode when dropped in the water from a helicopter, making aerial deployments impractical and undesirable.<ref name=Kelly />

The Mark 8 Mod 1 SDV has an endurance of about eight to 12 hours,<ref name=Davis /> giving it a range of {{convert|15|to|18|nmi|km|abbr=on}} with a diving team or {{convert|36|nmi|km|abbr=on}} without.<ref name="Jane's" /> The main limiting factor on endurance is not batteries or breathing gas for the SEALs, but water temperature:<ref name=Williams /> humans can only spend so much time in cold water, even with [[wetsuit]]s, before their blood pressure drops and they become dehydrated from losing blood volume and body fluids, respectively.<ref name=Kelly />
[[File:SDVmk9 SWA-Deck-Crew.jpg|thumb|left|US Navy SEALs deploy a torpedo-armed Mark 9 SDV from a submarine]]

===Mark 9 SDV===
Despite being a development of the Mark 8 SDV, the Mark 9 is a very different vehicle, designed for attacking surface ships rather than deploying SEAL teams on clandestine operations. Indeed, the Mark 9 and Mark 8 share very few common parts.<ref name=Klose /> The Mark 9 carries two SEALs, a pilot and a navigator, and two [[Mark 31 torpedo|Mark 31]] or [[Mark 37 torpedo]]es for standoff attacks against ships.<ref name=Williams>{{Cite book| publisher = Naval Institute Press| isbn = 9781612510064| last = Williams| first = Gary| title = SEAL of Honor: Operation Red Wings and the Life of LT. Michael P. Murphy (USN)| date = 2010-12-07| url=https://books.google.com/books?id=e8DnFCKgxzYC&pg=PA101| page=101}}</ref> These torpedoes can travel up to {{convert|3|nmi|km}} in a straight line,<ref name=Kelly98 /> carry a {{convert|330|lb|kg|adj=on}} warhead, and are capable of sinking ships as large as [[cruisers]].<ref name=Sutton>{{cite web |last1=Sutton |first1=H.I. |title=SDV Mk9: US Navy SEAL's torpedo armed mini-sub |url=http://www.hisutton.com/SDV%20Mk9.html |website=Covert Shores |access-date=20 September 2018 |date=21 August 2016}}</ref> In addition to torpedoes, the Mark 9 also carried [[limpet mine]]s and satchel charges in a large cargo compartment aft of the pilot and co-pilot.<ref name=Museum />

The Mark 9 is designed to clandestinely approach enemy vessels while submerged, surface to fire torpedoes, and then escape unnoticed. As such, its design incorporates [[Stealth technology|stealth]] characteristics, including a lower profile and sonar absorbing materials.<ref name=WalshWalker>{{Cite book| publisher = Simon and Schuster| isbn = 9780671868536| last1 = Walsh| first1 = Michael J.| last2 = Walker| first2 = Greg| title = SEAL!: From Vietnam's PHOENIX Program to Central America's Drug Wars : Twenty-six Years with a Special Operations Warrior| date = 1994| url=https://books.google.com/books?id=gMgxIvUz104C&pg=PA43}}</ref> The Mark 9 SDV was intended to attack ships in shallow coastal waters that full-size submarines could not enter,<ref name=Museum /> and to draw attention of an enemy fleet away from the Mark 9's parent submarine.<ref name=Sutton /> Though it proved very effective in exercises, the Mark 9 was retired starting in 1989 and was fully phased out of service by the mid-1990s due to manpower and budget constraints and because all of its capabilities save launching torpedoes were duplicated by the Mark 8.<ref name=Museum />

The pilot and navigator operate the vehicle from a prone position and lay side by side. The prone position gave the Mark 9 a low profile and enabled it to operate in very shallow water,<ref name=Kelly>{{Cite book| publisher = Open Road Media| isbn = 9781504047456| last = Kelly| first = Orr| title = Special Ops: Four Accounts of the Military's Elite Forces| date = 8 August 2017| url=https://books.google.com/books?id=rTotDwAAQBAJ&pg=PT123}}</ref> although SEALs reported that staying prone for the entire duration of an operation was uncomfortable.<ref name=Sutton />

The Mark 9's sleek profile and independent [[diving planes]] enabled it to be especially agile.<ref name=Sutton /> It was also faster than the Mark 8, reaching speeds of {{convert|7|-|9|kn|kph}}, owing to its twin [[screw propeller]]s and high-performance [[silver-zinc batteries]].<ref name=Museum /> Its speed and agility led operators to compare it to flying a fighter jet or driving a sports car.<ref name=Kelly />

[[File:US Navy 060206-N-1464F-003 A SEAL Delivery Vehicle (SDV) is loaded aboard the Los Angeles-class fast attack submarine USS Dallas (SSN 700) in preparation for a Special Warfare Training exercise.jpg|thumb|A Mark 8 SDV is loaded aboard ''Los Angeles''-class submarine {{USS|Dallas|SSN-700|6}}]]