seal delivery vehicle teams' historical roots began during wwii with the earliest human torpedoes to see use: maiale, used by italy's decima flottiglia mas, and chariots, used by british commando frogmen. naval special warfare entered the wet submersible field in the 1960s when the coastal systems center in panama city, florida developed the mark 7, a free-flooding sdv of the type used today, and the first sdv to be used in the fleet. the mark 8 and 9 followed in the late 1970s.