Concertina Wire

Concertina wire is barbed wire or razor wire formed into large coils that expand like the folds of a concertina, used as a rapidly deployable defensive barrier by militaries and, outside combat, at prisons, detention facilities, and borders. In the First World War soldiers improvised an early form by hand-coiling ordinary barbed wire around stakes; the modern self-supporting design, needing no vertical posts and able to stretch to fifty feet per coil, was created in the 1930s by the German engineer Horst Dannert using high-grade steel. Its chief military advantage is speed: a small unit can lay roughly a kilometer of barrier an hour, since the coils pack flat for transport and open quickly into an obstacle, and triple-coil arrangements build a more formidable barrier faster than driving stakes and stringing wire by hand.