Despite the obliteration of trench lines, by stupendous Allied artillery bombardments, the value of trenches as boundaries and rallying-points remained and as labour became available, new back lines and switch trenches were dug, sited according to the principles used by Loßberg in Champagne in late 1915. An artillery observation line was chosen and then a main line of resistance was dug in front, behind a crest overlooked by the observation line. Outposts were built along the crest, for infantry observers and listening-posts. Another line was built further back near the field artillery, which became known as the (artillery protection line), ready to be occupied by reserves, if the forward area was overrun. Command and supply became more difficult in such dispersed defences, which led to a streamlining of the chain of command, with battalion commanders being given sole authority over an area, as the . Division commanders were given similar control of the forces in the divisional sector, except for aviation units and some heavy artillery being used for special tasks.