Trench warfare
Trench warfare occurred when a revolution in firepower was not matched by similar advances in mobility, resulting in a grueling form of warfare in which the defender held the advantage. On the Western Front in 1914–1918, both sides constructed elaborate trench, underground, and dugout systems opposing each other along a front, protected from assault by barbed wire, mines, camouflaged trapping pits, and other obstacles. The area between opposing trench lines (known as "no man's land") was fully exposed to artillery fire from both sides. Attacks, even if successful, often sustained severe casualties.
Trench map
The earliest trench maps dating from 1915 were often made from enlargements of French and Belgian maps of variable quality. Some re-surveying of the front was carried out when it was found that such enlargements were not sufficiently precise. Precision was paramount to the artillery, especially later in the war when techniques were developed to "shoot from the map".