Jet Propulsion in Ballistics With Gravity Assist

So my idea is that from like 20,000 feet in the air there is an unmanned aerial bomber maybe like an airship. I basically want to attach a jet engine to a retractable tether, use the jet engine to launch ballistics and maintain the jet engine. It would dramatically reduce the cost to forcibly demolish a city where the typical military would have to use over 10,000 jet engines I could use one over a longer duration of time.