After Pearl Harbor, Boeing Plant No. 2 in Seattle (where B 17 bombers were built) was put under heavy camouflage to prevent a Japanese aircraft attack. The roof of the huge plant was covered with fake houses, streets, and trees. No Japanese planes came anywhere near the factory (my Mom was a riveter there before she enlisted). The plant is under the darker area in the center of the above photograph. The middle shot shows employees hanging out on the roof, and a view of the roof from street level.
A closer view of the 35-acre roof of Boeing Plant 2, with homes built of canvas, trees and shrubs made of board and mesh, and streets of oil and dirt:
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