
Revealing mistake: When Wade gets shot, watch the shot where Upham brings the bags up to the injured medic. The next shot there is some fog which then reveals the injured medic. In this shot, watch carefully as the cast rips away the medic's shirt. If you look near the neck, you can see the fake stomach vest he is wearing for a split second - when the actor realises he ripped too far up, he quickly covers it back up. (01:28:43)
Answer: These were barrage balloons, commonly used during the war. They are used to stop low level bombing and low level fly bys by enemy fighter planes. The cables attached to the balloons are designed to cut through the wings of the aircraft and to bring them down, so any pilot would have to fly above them, and the balloons would also restrict the view from above.