What happens when somebody else develops a drone to catch & return grenades thrown in through your window?
They profiled a new type of drone which is basically a human-controlled missile. Fly it right into a window!
Make 1000 of them ($5 000 000 is sth like 1 tank), put them in groups of 20 in 50 places where you suspect enemy will attack. Program them to wait with sensors on, when they detect enemy tanks they go up, land on tanks and explode. Tanks usually have much less armor on the top.