The Special Patrol Insertion/Extraction (SPIE) system was developed as a means to rapidly insert and/or extract a reconnaissance patrol from an area that does not permit a helicopter to land. SPIE has application for rough terrain as well as water inserts/extracts. It is an adaption of the Vietnam War-era STABO rig.
Generally, the SPIE rope is lowered into the pickup area from a hovering helicopter. Patrol personnel, each wearing a harness with an attached carabiner, hook up to a D-ring inserted in the SPIE rope. A second safety line is attached to a second D-ring located above the first. The helicopter lifts vertically from an extract zone until the rope and personnel are clear of obstructions, then proceeds in forward flight to a secure insert zone. The rope and personnel are treated as an external load and airspeeds, altitudes, and oscillations must be monitored.
The United States Coast Guard uses a similar technique to board ships when speed and stealth are required.