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
For much of the Great War, trench warfare was almost static, giving rise to the need for large scale maps for attack, defence and artillery use. Initially, British trench maps showed the German trench systems in detail, but only the British Front line. Later in the war, more of the British trenches were shown. The only British maps that showed full detail of both sides were the secret editions, usually marked "Not to be taken beyond Brigade HQ" for fear of their falling into enemy hands.