This Great War period guide to the art of flag semaphore was original published by Gale & Polden and formed part of their respected "Military Series." Each letter of the alphabet is illustrated with a front facing soldier using this rapid means of field communication. Semaphore could usefully be employed at short distances, as between columns and their advanced guard, or rear guards, across rivers, or fire swept zones, and to connect an attacking line with its supports. Flag semaphore is the telegraphy system conveying information at a distance by means of visual signals with hand-held flags. Information is encoded by the position of the flags; it is read when the flag is in a fixed position. Semaphores were adopted and widely used in the 19th century.