coffin deep under the water." A 2011 article reported that out of 2,600 SEALS roughly 230 are trained to operate the SDVs. SDVs are generally launched from a Dry Deck Shelter on the back of a submarine, although they can also be deployed from amphibious carriers and other surface ships equipped to launch and recover the SDV. SDVs are launched and recovered by surface ships using a crane. They can also be airdropped (uncrewed) into an operational area from a C-130 Hercules airplane. Finally, the SDV can be launched from the shore. An SDV can be launched from one platform and recovered by another. demonstrated this capability during a multilateral exercise in the Mediterranean when it recovered and then launched another country's SDV. 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. Its updated electronics, materials, and battery and motor systems gives it twice the range and 1.5 times the speed of the Mod 0. 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. 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. The Mark 8 Mod 1 SDV has an endurance of about eight to 12 hours, giving it a range of with a diving team or without. The main limiting factor on endurance is not batteries or breathing gas for the SEALs, but water temperature: humans can only spend so much time in cold water, even with wetsuits, before their blood pressure drops and they become dehydrated from losing blood volume and body fluids, respectively. 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. The Mark 9 carries two SEALs, a pilot and a navigator, and two Mark 31 or