SHADOWLESS BUILDINGS
Any projection above the ground was apt to cast a shadow which would show up on the observer's photographs. This was a difficulty that was experienced in building the hangars for airplanes. The roofs of these sheds were painted green so as to match the sod around them, but as they projected above their surroundings, they cast shadows which made them clearly evident to the enemy. This was overcome by the building of shadowless hangars; that is, hangars with roofs that extended all the way to the ground at such an angle that they would cause no shadow except when the sun was low. In some cases, aëroplanes were housed in underground hangars, the approach to which was concealed by a canvas covering. As for the machines themselves, they scorned the use of camouflage. Paint was little protection to them. Some attempt was made to use transparent wings of cellon, a material similar to celluloid, but this did not prove a success.