1. The prefabricated harbor consisted of three main elements. The breakwater (A) was made of a chain of great concrete caissons and blockships, sunk to form a shelter for the cargo ships as they dock at the pierheads (B) where they unload. The cargoes are carried on vehicles along the floating roadways (C) that run from the pierheads to the shore-ramps onto the land. (Note in picture above that the sea is rougher outside the caissons. Note also the barrage balloons above the caissons.