DARPA just started its "Inbound, Controlled, Air-Releasable, Unrecoverable Systems" (ICARUS) program, which involves single-use drones that "fall apart into disposable usefulness" once they're done doing their job. These specially designed drones will vanish within four hours and should be able to drop 3lb. packages within 32ft. of their target. The total wingspan of the drone should be less than 10 feet while also being capable of being released from 35,000 feet and flying 90 miles.
To accomplish this feat, DARPA has committed $8 million for a two-phase project that will last over 26 months. They are optimistic that they'll be able to address the "capability gap in eliminating the leave-behind of air vehicles used to deliver supplies to personnel on the ground without requiring pack-out." ICARUS is built on another program, VAPR, which created electronics that dissolve in water or on command. DARPA is planning on making meltability a feature of the ICARUS drones.