The First World War was the most devastating in British military history, with nearly 800,000 men killed and over two million wounded. Early in the war, the BEF was virtually destroyed and was replaced first by volunteers and then by a conscript force. Major battles included those at the Somme and Passchendaele. Advances in technology saw the advent of the tank (and the creation of the Royal Tank Regiment) and advances in aircraft design (and the creation of the Royal Flying Corps) which would be decisive in future battles. Trench warfare dominated Western Front strategy for most of the war, and the use of chemical weapons (disabling and poison gases) added to the devastation.