Developments in artificial intelligence and automation will make it possible to operate massive drone fleets simultaneously, increasing efficiency and greatly expanding their capabilities.
Earlier this year, the country's Defence Advanced Research Projects Agency announced plans to pay Boeing to investigate formation flight, though the programme has yet to begin.
It might also be hard for airlines to co-ordinate the departure times and destinations of passenger aircraft in a way that would allow them to gain from formation flight.
There are reports that some military aircraft flew in formation when they were low on fuel during the Second World War, but Dr. Lissaman says they are unsubstantiated.