In the near future, US Army and Marine Corps infantry squads could march into battle behind swarms of hundreds of flying and crawling drones.

At least, that's the plan. On October 12, the Defense Advanced Research Projects Agency—the Pentagon's fringe-science wing—asked robot-developers to submit ideas for tactics and technologies that could allow small infantry units to deploy swarms of 250 or more robots.

The swarms must function "in built-up areas up to eight city blocks in size over mission durations of up to six hours," according to Dr. Timothy Chung, the program manager.

Chung's Offensive Swarm-Enabled Tactics initiative—a.k.a, OFFSET—overlaps conceptually with a separate military effort to deploy large formations of small drones from fighter jets. OFFSET also dovetails with DARPA's Squad-X program, which is trying to outfit infantry squads with better communications, sensors, and weapons.

The infantry's semi-autonomous drone swarms could help detect enemy forces and guide artillery and air strikes in and around densely-packed, tall buildings, DARPA explained. "Urban canyons—with their high vertical structures, tight spaces and limited lines of sight—constrain military communications, mobility and tactics in the best of times."

"Unmanned air vehicles and unmanned ground vehicles have long proven beneficial in such difficult urban environs," the agency added. "But their value to ground troops could be vastly amplified if troops could control scores or even hundreds—'swarms'—of these robotic units at the same time."

The major obstacle isn't the drones themselves. Wheeled and tracked ground robots and quadcopters are "increasingly capable and affordable," DARPA stated. But the US military lacks the technologies to manage drone swarms. The Marine Corps began issuing quadcopters to infantry squads in September, but the squads operate the quadcopters individually.