Page:Popular Science Monthly Volume 91.djvu/187

 Why the Hindenburg Line Seemed So Impregnable

���The victorious British have unearthed the se- cret of the strength of the Hindenburg line. It lay in concealed forts of solid cement hidden in the most ingenious ways. In the top picture one is seen built so as to seem part of a ruin

��One fort discovered by the British was built under an old barn. It was covered over with grass and was entered by means of the ladder and pulley arrangement shown above. It was used as a station for a machine gun

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