The first and greatest lesson of the war, then, is this—that the value of an effective navy, when the time comes for it to manifest its effectiveness, is out of all proportion to the sums, vast though these may be, that it has cost; that if it overmatches the opposing navy decisively enough, the country behind it may rest secure and serenely indifferent to the thought of invasion or even of attack, so far as its sea frontier is concerned; and that the navy—still assuming it to be of commanding strength—may accomplish its whole mission of defense without ever being called upon to strike a blow.
It can hardly be necessary to point out the fact that this lesson may be read in terms of "preparedness." The British navy was prepared when the war began; the British army was not. The German army was prepared; the German navy was not—in the sense of being large enough for its mission. With these facts in mind, we have only to look at the contrast between the progress of the war on land and that on the sea to read the whole lesson of preparedness in a form so concrete that it is hard to understand how any observer can fail to grasp its full significance.
Among the minor lessons of the war, it will probably appear to most laymen that the unforeseen effectiveness of the submarine is the most significant. In a way this is true; but the significance of the lesson may be dangerously exaggerated unless we recognize the part contributed to the early successes of the submarine by the element of surprise to which allusion has already been made. When the war began, the submarine was an untried and an almost unknown weapon, and the British navy was rather contemptuous of it, or at least indifferent toward it. Its dramatic appearance in the North Sea at early dawn of a misty September morning was as great a surprise to the three British cruisers which it sank in rapid succession as the story of the disaster was to the world at large. The fact that the cruisers by their carelessness invited the fate which came to them does not, of course, deprive the incident of significance. But after all, the world has never doubted that a submarine could sink a ship that practically insisted upon being sunk.
As a result of this experience, British men-of-war operating thereafter in what they considered submarine territory, took reasonable precautions; and in such waters no other important successes have been scored against them. But neither to them nor, probably, to anyone else except their adversaries, did it occur that a submarine could make its way from the North Sea to the Dardanelles. And so it came about that when one of them appeared there, it found conditions again ideal for surprise, and taking advantage of these conditions delivered its attack and scored a success as striking as the earlier one in its own home waters.
The activities of submarines against merchant shipping we need not discuss here. The only lesson they hold for us, from the point of view of naval warfare, is the lesson that for them, as for all other activities of the submarine, there is an answer. The answer was not ready when the war began, but it was not long delayed. We are apt to think of the submarine as if it always operated under water, and completely under water. But when it is completely under water, it is completely blind and as helpless as other blind things are. To see objects at a distance, it must be on the surface, and to see them even close at hand it must at least expose its periscope. Having definitely located an object within easy range, it may wholly submerge and deliver its torpedo without seeing the target. But the chance of a hit under these conditions is remote. Normally the submarine remains on the surface until it sights an enemy. Having approached as close as seems practicable without danger of being seen itself, it submerges, except for the periscope, and approaches within range, directing its course and its aim, by sight—not by some occult instinct such as is often attributed to it. When within a zone where imminent danger threatens, it may remain wholly submerged for a long period of time, but when so submerged, it is not in any degree a threat to other craft.
In other words, the submarine is dangerous only when it can see. And when it can see, it can be seen—not easily perhaps, but certainly by an observer reasonably close at hand and on the lookout. It is especially liable to detection from an airship. Moreover, the noise of its propellers can be heard at a considerable distance, and a very sensitive microphone has been developed as a submarine detector. The waters about Great Britain are now patrolled by hundreds of small, fast craft—destroyers, trawlers, motor boats—always on the lookout for a periscope or other indication of the proximity of a submarine. If one is actually seen, its capture or destruction follows as a matter of course. If the presence of one is indicated by the microphone or other evidence, such as oil floating on the water, or bubbles rising to the surface, nets are lowered and the water dragged for miles around. It is not known how many submarines have been destroyed by these tactics, but the number is unquestionably large. Thus the submarine is being robbed of much of its mystery and much of its terror, and while it remains, and will always remain, a danger, the lesson of the war is that it must take its place beside other dangers with which modern war is filled, as something to be respected and feared, but not as having rendered the battleship and battle cruiser obsolete.
Another lesson of the war has resulted from the fact that practically all of the important operations on the British side have been conducted by battle cruisers, not by battleships. It is not to be understood from this that the battleship has been discredited, for such is not the case. The fleet to which reference has already been made as holding the gates of the North Sea and "containing" the German fleet behind the fortifications of Helgoland is made up principally of battleships, and it is largely because they have been engaged in this important duty that the few opportunities which the war has offered for active service have fallen to the lot of battle cruisers. But there are other reasons for this which spring from the nature of the battle cruiser itself and inhere in the difference between this type and the battleship. In size the types are practically identical, and in power of armament the difference is not great. But the battle cruiser sacrifices much of the armor by which the battleship is weighted down, and purchases by this sacrifice a great increase in speed. The typical battleship of to-day has some 14 inches of armor on the side; the battle cruiser, from 5 to 9 inches. The battleship has 22 knots speed, the battle cruiser 32 knots. There has been much discussion as to the relative merits of the two types, and conservative officers have been slow to accept the battle cruiser. The war has shown the necessity for both types, and no better illustration of their relative merits could be wished than that which is afforded by the spectacle of the battleships engaged in what is practically a blockade of the German fleet, while the battle cruisers have swept the German raiders, the Scharnhorst, Gneisenau, and their consorts, from the distant seas which were the chosen field of their operations. Following the destruction of Admiral Cradock's little squadron by the faster and more heavily armed Scharnhorst and Gneisenau, the British admiralty dispatched a squadron of battle cruisers to run down the German ships, and in the battle off the Falkland Islands the history of Coronel was repeated with a change of sides, the fast and heavily armed battle cruisers under Admiral Sturdee making short work of the German ships, which they overmatched in speed and range as decisively as the Germans had overmatched the ships of Admiral Cradock's squadron at Coronel. In each case victory went to the ships of high speed and long-range guns, and these two are the determining characteristics of the battle cruiser. In the action of January 25, 1915, in the North Sea, the same characteristics won again. Battle cruisers were engaged on both sides, but the side which had the advantage in speed and range won the fight.
Thus the battle cruiser had justified itself, and its justification is one of the striking lessons of the war. We may believe that the lesson will be emphasized if the time ever comes when this type finds the opportunity to display its adaptability for work in certain other fields for which it was originally designed—in scouting operations, for example, and in flanking movements in connection with a fleet engagement.