“Official photo of the recent English progress at the Western Front. A well hidden trench,” between 1914 and 1918, via Nationaal Archief (of the Netherlands) Commons on flickr.
It occurred to me that some, or a lot, of the wattle could have been woven by men who were gardeners before the war.
WWI trenches were not actually straight, but zigzagged to prevent enemy soldiers from firing down the axis. They were normally about 4 m. (12′) deep.