The development of the flash signaling, adopted in the British navy in 1867, was an adaptation of the Morse code to lights.
The first application of the telegraph in time of war was made by the British in the Crimean War in 1854, but its capabilities were not well understood, and it was not widely used.
In addition to its employment in spanning long distances under the civilian-manned military telegraph organization, mobile field service was provided in the Union army by wagon trains equipped with insulated wire and lightweight poles for the rapid laying of telegraph lines.
Immediately before and during the Civil War visual signaling also received added impetus through development of a system, applying the Morse code of dots and dashes, that spelled out messages with flags by day and lights or torches by night.
The fact that commanders could not control, coordinate, and direct huge modern armies without efficient signal communication quickly became apparent to both the Allies and the Central Powers.
The Germans, despite years of concentration on the Schlieffen Plan, failed to provide adequately for communication between higher headquarters and the rapidly marching armies of the right wing driving through Belgium and northern France.
The organization and efficiency of the armies varied greatly.
At one end of the scale was Great Britain, with a small but highly developed signal service; and at the other end stood Russia, with a signal service inferior to that of the Union Army at the close of the American Civil War.Simultaneously, the Prussian and French armies also organized mobile telegraph trains.During the short, decisive Prussian campaign against Austria in 1866, field telegraph enabled Count Helmuth von Moltke, the Prussian commander, to exercise command over his distant armies.Another development for light signaling placed a movable shutter, controlled by a key, in front of a strong light.An operator, opening and closing the shutter, could produce short and long flashes to spell out messages in Morse code.The Prussian army in 1833 assigned such visual telegraph duties to engineer troops.