German reconnaissance aircraft surveyed all of the Western Front over the winter of 1916–1917 to look for signs of Anglo-French offensive preparations. The design of the (Siegfried Position, later known by the Allied powers as the Hindenburg Line) was drawn up by Colonel Kraemer, an engineer from supreme headquarters (OHL) and General Lauter, the Inspector General of Artillery. Construction was organised by Rupprecht and Kuhl; when the plans were ready the line was divided into sectors and officers from the General Staff, gunners and engineers were appointed to oversee construction, which was expected to take five months. The defences were built by German construction companies, who brought skilled workmen to fabricate ferro concrete emplacements, while and labourers and Russian prisoners of war dug the trenches. The building works absorbed most of the cement, sand and gravel production of occupied France and Belgium plus that of west Germany. Transport of materials was conducted by canal barge and railway, which carried of engineering stores, although the building period from October 1916 to March 1917 meant that only about eight trains a day were added to normal traffic. Mass-production techniques were used to produce items for the position. Steel-reinforced concrete dug-outs for infantry squads and artillery-observation posts were standard designs and all woodwork was made to a pattern.