[coryfklein]

The main reason cheap drones are effective is because they come from fast-moving consumer product lines instead of the slow-moving monolithic military industrial complex side.

There is nothing fundamentally indefensible about drone swarms, the complex just hasn't had enough time to react. You can bet that, if it doesn't already exist in secret somewhere in the US, there are many teams actively working on tank-mounted drone laser defense systems.

I suspect that drones have been hard to target until now because they have a unique air signature far different from all previous air targets, not because they are fundamentally more "invisible" than a Predator or a helicopter. Given their unique shape, movement, noise, and radio profile, a CS grad could certainly cobble together a drone target acquisition system using some consumer-level optic systems combined with a radio antenna, radar, and microphone array.

And as we all know, quadcopter drones are exceedingly fragile and most of their profile is millimeter-thin plastic blades. Once you have the ability target them, you'd only need a moderately powered laser to completely disable them.