5925437 British troops in the trenches, 1914 (lantern slide) by Unknown photographer, (20th century); National Army Museum, London; (add.info.: British troops in the trenches, 1914. Lantern slide, World War One, Western Front (1914-1918), 1914. The First Battle of Ypres (20 October-22 November 1914) marked the end of open warfare on the Western Front. Both sides dug in and a line of trenches 466 miles in length soon ran from the Channel to the Swiss frontier. These early trenches were built quickly and tended to be simple affairs that offered little protection from the elements. From a box of 72 lantern slides.); by National Army Museum .