Helicopter Rope Suspension Technique
Helicopter Rope Suspension Technique (HRST) is a military term for techniques and methods of rappelling, fast roping, Special Patrol Insertion/Extraction (SPIE) and Jacob's Ladder operations. Helicopter Rope Suspension was developed as a means to insert and/or extract, by helicopter, ground forces (primarily reconnaissance teams) into or from rough terrain, urban areas or water.
Source: Wikipedia — Helicopter Rope Suspension Technique (CC BY-SA 4.0)