Drone delivery — tied up in regulatory debates and largely nonexistent beyond a few, isolated pilots — hasn't boomed in the U.S. yet, but Amazon and Walmart are placing big bets on unmanned vehicles. The big picture: The hooplah has intensified to the point where a number of upstarts are popping up to offer drone-delivery-in-a-box to the retailers who can't afford to invest themselves. The two retail rivals are betting that drone delivery — currently estimated to be worth $30 billion — will take an increasingly large share of the $1.5 trillion logistics business."The market for drone logistics can be tremendous," says Sertac Karaman, a professor at MIT.What's happening: Amazon stole the headlines last week when it debuted a brand new package delivery drone at its annual re:MARS conference. But the e-commerce titan has a worthy opponent in Walmart, which has actually outpaced Amazon in the drone patent race in 2018 and 2019, per the FT.Amazon envisions using drones to make thousands of super-fast deliveries from warehouses that are on the outskirts of cities to doorsteps, skipping all the traffic jams.Walmart, with its 5000-store footprint, could use drones to challenge Amazon's delivery prowess and transport millions of bags of groceries in minutes.And the two could force other smaller retailers to use drones in order to compete. There are already companies hoping to capitalize on this need, Karaman says. Top Flight Technologies in Boston makes drones and the software that powers them. Another called Flirtey is offering drone delivery as a service.Worth noting: Chinese companies are far ahead of their American counterparts when it comes to delivery by air. Chinese e-commerce giants JD.com and Alibaba have used drones to transport packages to China's hinterlands since 2016.