Original sentence: According to a former intelligence official, during the mid 1990s, the NSA with the help of the Navy installed a tap on a fiber optic line using a specially equipped spy submarine.Also, submarine cables carry 10,000 volts of power.An intelligence official estimated that tapping all the world's undersea cables would cost more than $2 billion a year.Describing the submarine used, a former intelligence official said that "It's a submarine capable of bringing a length of cable inside a special chamber, where the men then do the work," while the sub hugs the ocean floor.Fiber cables normally lie in a trench dug 3 feet deep into the ocean bed unless of course the cable lies more than 1000 feet below the surface in which case they are left to lie exposed on the ocean floor.For a successful tap, the cable must be sliced which makes detection possible.However, the NSA's computers of that decade were unable to handle the flood of data from the tapped cable.In 1998, Congress agreed to enlarge the sub with what the Navy called "advanced technology for naval special warfare and tactical surveillance.NSA officials say that they believe the operation went unnoticed.Such a task is difficult to accomplish.The NSA in conjunction with the Navy proposed equipping the USS Jimmy Carter with such a special chamber as part of a "special operations" upgrade to the $2.4 billion sub.The details of this are sketchy and the results reportedly mixed.Using this  specialized sub, they descended hundreds of feet and sliced a fiber optic cable in one of the world's ocean