AMAZON has long talked about using drones to deliver parcels, but a patent recently uncovered shows its big-picture plan: airborne warehouses flying over cities armed with fleets of drones for delivery products on demand.

Amazon earlier this month announced it had made the first successful delivery by drone, shipping a small parcel to a customer in Cambridge.

The patent, granted by the US patent office in April but only uncovered this week by tech analyst Zoe Leavitt, describes motherships floating above cities that release drones that save energy by dropping with gravity before kicking in with their motors.

The patent describes a range of uses for the flying warehouses, including flying above a football game and loaded with sporting paraphernalia and food products that spectators at the game could order and get delivered instantly by drone.

"Perishable items or even prepared meals can be delivered in a timely fashion to a user," the patent says.