As their rivalry intensifies, U.S. and Chinese military planners are gearing up for a new kind of warfare, air and sea drones equipped with artificial intelligence. The planners envision a scenario in which hundreds, even thousands of the machines engage in coordinated battle. The Pentagon is pushing urgent development of inexpensive, expendable drones as a deterrent against China acting on its territorial claim on Taiwan. Washington says it has no choice but to keep pace with Beijing. The unchecked spread of swarm technology “could lead to more instability and conflict around the world,” said Margarita Konaev, an analyst with Georgetown University’s Center for Security and Emerging Technology.