At any hour the enemy may suddenly decide to attack and they may find their houses pounded down about their heads and perhaps half of a company wiped out in a quarter of an hour. Then other communication trenches lead back until finally you are in the open country out of the range of bullets, but not outside the range of shells. Here the munition caissons and the transport wagons come up by night bringing the food for men and guns which is taken up to the hungry mouths under the cover of darkness; and here, on an average day, one will occasionally observe the passing of an ambulance with its green roof and sides which melts it into the road and the landscape—and processions of ambulances when there is battle. All the detail of army existence is as precise as that of the best organized industrial plant.
As you walk along you will spy at intervals a hidden battery, perhaps in a house, perhaps in a hedge, perhaps in a group of trees, perhaps beautifully roofed over with sod, so that it is invisible from the air. You rarely look up without seeing an aeroplane flying overhead. When there is action, you will see many. A faint pur comes out of the heavens and two planes are seen circling as they exchange bullets from their machine guns. Another plane is turning to the right and left and ducking to avoid the thistle blows of smoke which burst from the shrapnel shells fired by the antiaircraft guns.
Follow the course of the long procession of motor trucks which feed the army and you arrive at one of the great supply depots which every day send out the precise quota of supplies that are needed, with every motor truck having its schedule and keeping that schedule with the accuracy of a first-class passenger train. Follow the ambulances back from station to station, where the wounded men are examined to see if they are suffering from a hemorrhage and whether they are able to stand the farther journey and do not need an immediate operation, and you are brought to the immense base hospitals in a closely guarded and well ordered camp where every sanitary tradition known to modern life is absolutely enforced. One of these hospitals had twelve thousand beds and in the offensive of September 25, 1915, it discharged seven thousand patients in a day.
Soldiers are restricted to the neighborhood of their billets and officers themselves must have passes if they travel outside the region occupied by their battalions. Everyone is a policeman under an intricate system guarding every detail of army secrets from any spy and from those gallant aviators who risk antiaircraft gunfire in the hope of bringing home some information to their side.
Never has the Intelligence Service of an army had so many secrets to guard; never has it required such complicated measures of protection against espionage. In Napoleonic times, it was enough to know that your adversary was marching a hundred thousand men along parallel roads. This your cavalry scouts might discover; or a spy who had crossed the frontier in an unfrequented place might be watching the enemy's army and counting his numbers as they passed. Now the frontier is an intact line of trenches.
The spies of Richelieu's day have been surpassed in this, our day—with their stories yet to be told. Many a man who spoke the enemy's language well has put on the enemy's uniform, joined one of his scouting parties between the trenches in the darkness, entered the enemy's trenches, heard all the talk and slipped back to his own lines safely. If apprehended, his fate was certain—death.
The most efficient spy, of course, is the one with military training He knows the value of what he sees. Usually he is an officer of good family who has been cashiered for gambling or debt and takes a desperate chance out of patriotism and the hope of atonement. Naturally, the easiest route for spies was through Holland and Switzerland which became the gateway of passing spies and the playground of espionage and counterespionage. Gradually the restrictions tightened for all neutral travelers from capital to capital, while none were permitted to go into the zones of the armies, some twenty or thirty miles from the trenches.
The problem of the Intelligence Corps is much like that of putting the parts of a picture puzzle together. A line from a newspaper in one part of the world, a line from a newspaper in another taken in connection with a photograph, an excerpt from a letter found on a prisoner or a fact got from a prisoner by skillful catechism, might develop a valuable contributory item. The amount of information procured by either side about the other was only less amazing to the outsider than how it was obtained. Again, events revealed amazing ignorance. Most baffling and most secret of all branches is this, whose work is both gaining and conserving information, and just as professional, just as carefully prepared before the war as any other.
A single instance illustrates how small a fact may be of value to the enemy. A certain well known "military expert" went out to British headquarters as a guest of a general. From a tower in the square of a small town, he watched a certain action. When he wrote his account of it, it was submitted to the general who was his friend; and the general carelessly passed one little statement which no Chief of Intelligence of any army would ever have passed and probably no correspondent of experience would have had the temerity to submit to the censor unless he wanted to be responsible for the death of men who were his hosts and his friends. For the writer stated that he saw the battle from this tower.
Now the London papers reach Holland at four o'clock in the afternoon where they are seized promptly by the tentacles of the German Intelligence Service, which did not need to undertake any "picture puzzle work" on this occasion. It was plain as day that this tower must be used as an artillery observation post by the enemy. From there he could see the fall of shells from his batteries and know whether they were "on" or not. Out of the blue sky the next morning, came a German artillery concentration which brought the tower down like a house of cards, and many British soldiers billeted in the neighborhood were killed or wounded.