midnight
What was this thing which they were about to do ? Through the windows , at a distance of four hundred yards , the pounding of the machinery which flooded the water jacket of the Relay Gun was distinctly audible in the stillness of the night . The pressure of a finger -- a little finger -- upon that electric button was all that was necessary to start the torrent of iron and high explosives toward Paris . By the time the first shell would reach its mark nine more would be on their way , stretched across the midnight sky at intervals of less than eight miles . And once started the stream would continue uninterrupted for two hours . The fascinated eyes of all the officers fastened themselves upon the key . None spoke .