section_path: Progress of the war/Western Front 1914 to 1916/Trench warfare begins
section_name: Trench warfare begins
paragraph_text: Trench warfare begins
  
  Pre-war military tactics that had emphasised open warfare and individual riflemen proved obsolete when confronted with conditions prevailing in 1914. Technological advances allowed the creation of strong defensive systems largely impervious to massed infantry advances, such as barbed wire, machine guns and above all far more powerful artillery, which dominated the battlefield and made crossing open ground extremely difficult. Both sides struggled to develop tactics for breaching entrenched positions without heavy casualties. In time, technology enabled the production of new offensive weapons, such as gas warfare and the tank.
  
  After the First Battle of the Marne in September 1914, Allied and German forces unsuccessfully tried to outflank each other, a series of manoeuvres later known as the " Race to the Sea ". By the end of 1914, the opposing forces confronted each other along an uninterrupted line of entrenched positions from the Channel to the Swiss border. Since the Germans were normally able to choose where to stand, they generally held the high ground, while their trenches tended to be better built; those constructed by the French and English were initially considered "temporary", only needed until an offensive would destroy the German defences. Both sides tried to break the stalemate using scientific and technological advances. On 22 April 1915, at the Second Battle of Ypres, the Germans (violating the Hague Convention) used chlorine gas for the first time on the Western Front. Several types of gas soon became widely used by both sides and though it never proved a decisive, battle-winning weapon, it became one of the most feared and best-remembered horrors of the war.