The SDV MK 7 was the first successful submersible designed and produced by the U.S. Navy. Its occupants wore a form of oxygen rebreather that eliminated the bubble tail, and its vertical design produced considerable stability and maneuverability. Navy Special Operations Forces and Underwater Demolition Teams used the SDV MK 7 during the late 1960s and early 1970s, including in the Vietnam War. Before 1968, the U.S. Navy imported SDVs from abroad, where they had been developed and perfected for many years.