Medical Unit, Self-contained, Transportable (MUST) was a type of medical equipment system developed for field hospitals in the United States Army in the late 1950s and early 1960s. The system used inflatable shelters for ward and patient care space, and expandable shelters for operating rooms and other sections. They were powered by auxiliary power units which used JP-4 as fuel, producing power and air conditioning for the hospital in addition to air to keep the shelters inflated. A 60-bed surgical hospital in Vietnam could use up to 3,000 gallons of JP-4 per day to keep the hospital inflated and operational.