"The Air Force measures its UAV capability by the number of targets it can watch around the clock. Keeping one drone over one target is called an orbit, or combat air patrol (abbreviated CAP ). Each CAP generally requires four aircraft, a control station, antennas, and satellite communications — plus pilots, intelligence operators, maintainers, and more."
"No matter how fast the Air Force buys the drones, the service cannot train pilots and mission technicians quickly enough to meet the ever-growing demand... Their services are so valuable that the Air Force’s request to reduce its CAPs required the approval of Defense Secretary Ashton Carter. The long-term viability of the UAV force factored into the decision-making process."