Danton, Louis (1915). "Cubisme et camouflage - L'Histoire par l'image". histoire-image.org (in French). Retrieved 18 August 2012. Example of observation tree made of steel and painted metal sheets at Armancourt (Somme) in March 1915.
lrb.co.uk
Wright, Patrick (23 June 2005). "Cubist Slugs". London Review of Books. 27 (12): 16–20.