Artillery pieces were soon painted in contrasting bold colours to obscure their outlines. Another early trend was building observation trees, made of steel with bark camouflage. Such trees became popular with the British and French armies in 1916. The observation tree was invented by French painter Lucien-Victor Guirand de Scévola, who led the French army's camouflage unit, the first of its kind in any army. He also invented painted canvas netting to hide machine gun positions, and this was quickly taken up for hiding equipment and gun positions from 1917, 7 million square yards being used by the end of the war. The First World War also saw the birth of aerial warfare, and with it the need not only to conceal positions and vehicles from being spotted from the air, but also the need to camouflage the aircraft themselves. In 1917, Germany started using a lozenge camouflage covering Central Powers aircraft, possibly the earliest printed camouflage. A similarly disruptive splinter pattern in earth tones, "Buntfarbenanstrich 1918", was introduced for tanks in 1918, and was also used on the Stahlhelm (steel helmet), becoming the first use of a standardized camouflage pattern for soldiers. In 1909 an American artist and amateur zoologist, Abbott Thayer published a book, "Concealing-Coloration in the Animal Kingdom", which was widely read by military leaders, though his advocacy of countershading was unsuccessful, despite his patent for countershading submarines and surface ships. The earliest camouflage artists were members of the Post- Impressionist and Fauve schools of France. Contemporary artistic movements such as cubism, vorticism and impressionism also influenced the development of camouflage as they dealt with disrupting outlines, abstraction and colour theory. The French established a "Section de Camouflage" (Camouflage Department) at Amiens in 1915, headed by Lucien-Victor Guirand de Scévola. His "camoufleurs" included the artists Jacques Villon, André Dunoyer de Segonzac, Charles Camoin and André Mare. Camouflage schemes of the First World War and Interwar periods that employed dazzle patterns were often described as "cubist" by commentators, and Picasso claimed with typical hyperbole "Yes, it is we who made it, that is cubism". Most of the artists employed as "camoufleurs" were traditional representative painters, not cubists, but de Scévola claimed "In order to deform totally the aspect of the object, I had to employ the means that cubists use to represent it."