>barbed wire

On the topic i recently watched an interesting documentary on the problems at the battle of the Somme in WW1 https://youtu.be/CbkJS5cLLOQ?list=PLhMDlPcDRBKQuhPC9Ifj2IL8L... ( ~15min segment)

A short summary is the British assumption that massive artillery barrage would destroy the German defenses and allow for British troops to walk through easily. Unfortunately they used shrapnel shot which did very little to the defenses and worse, left the barbed wire installations untouched. Advancing troops then got stuck and were mowed down