This is a barrage balloon.

Goofy as it may seem, you do not fuck with a barrage balloon; a common sight during WWII, these unmanned dirigibles were hung in the sky trailing thick cables to deter low-flying enemy aircraft. Evidently the anti-aircraft guns of the day weren't fast enough to track and fire on fast-moving targets at low altitudes; thus the barrage balloons were deployed to force enemy aircraft skyward into the sights of the ground-bound AA guns.

Sometimes the Allies attached explosives to the drag cables, just to fuck low-flying bombers up that much more.