Recent releases of once secret files reveal the details of a 6-year CIA effort to salvage a Soviet submarine dubbed Project Azorian.
It's a heck of a story, and notable too for the formal non-answer reply to questions about policies and programs - "We can neither confirm or deny ..."
"Ultimately, the engineers opted for a plan that sounded like it was lifted from the plot of a James Bond film (actually, it did become the plot of a James Bond film). The plan involved three vessels: 1) An enormous recovery ship with an internal chamber and fitted with a bottom that could open and close. This ship would use a docking leg system that would, in effect, turn it into a stable platform for using a lifting pipe to raise and lower a 2)"capture vehicle" fitted with a grabbing mechanism that would be designed to align with the hull of the sub. The capture vehicle would be secretly assembled on a 3) massive barge with a retractable roof. The barge would be submersible, so that it could slip beneath the ocean, under the recovery ship, open its roof and deliver the capture vehicle — all the while remaining hidden from any potential reconnaissance."