A barrage balloon is a large balloon tethered with metal cables, used to defend against low-level aircraft attack by damaging the aircraft on collision with the cables, or at least making the attacker's approach more difficult. Some versions carried small explosive charges that would be pulled up against the aircraft to ensure its destruction. Barrage balloons were regularly employed only against low-flying aircraft, the weight of a longer cable making them impractical for higher altitudes.
In the opening days of the Race's Invasion, Barrage balloons ended up being the most effective anti air weapon against Killercrafts. This was due to flying so low and fast that they couldn't evade the balloon’s wires if they were in their flight path.