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.
Barrage (artillery)
Artillery usually fired over open sights at visible targets, until the Second Boer War when indirect fire started to be used. The largest unit accustomed to firing at a single target was the brigade (i.e. an artillery battalion), normally 18 guns. Trench warfare led to the necessity for indirect firing through the use of observers, more sophisticated artillery fire plans and an increasingly scientific approach to gunnery. Gunners had to use increasingly complicated calculations to lay the guns. Individual guns were aimed so that their fall of shot was co-ordinated with others to form a pattern; in the case of a barrage, the pattern was a line. The term “barrage” was first used in World War I in English in the orders for the Battle of Neuve Chapelle in 1915.