http://www.skylighters.org/barrageballoons/
Here’s a weapon of war that’s new to me: “The barrage balloon, filled with lighter-than-air gas, was attached to a steel cable that could be raised or lowered using a motorized winch. In forcing enemy planes to higher altitudes, surprise invasions became less likely and bombing accuracy was hampered as well. The balloons restricted the airspace available to rogue aircraft, channeling their flights into zones protected by ground-based artillery. The cables themselves presented a hazard to pilots, capable of shearing off a passing plane’s wings and propellers. “