In all wars, whether by sea or land, some few general lessons stand out unmistakably; but the difficulty of arriving at a just estimate of the relative significance of the causes which have led to victory or to defeat is always extreme. Genius, which may be defined as an unerring sense of proportion, is necessarily rare, and the person with an _idée fixe_ in favour of some particular method or weapon will generally discover, in every conflict, evidence in support of his faith. This tendency will be most marked when national experience of war is lacking, and we are, therefore, compelled to draw our inspirations from fighting carried on by other peoples. In the long series of wars which culminated in the Nelson era, broad principles had been evolved and had been grasped by the leaders of naval thought. More than ninety years have elapsed since the British Navy was called upon to fight a great fleet action, and meanwhile technical progress of all kinds, advancing by giant strides, has opened out new possibilities tending to bewilder the imagination and to invite mistakes and impolicy. Even when, as now, valuable war experience is available, there is always a risk of false deductions. Conditions differ so greatly that generalisations based upon special episodes may be misleading and even dangerous. Thus the American Navy and our own have unquestionably suffered from shallow reasoning derived from the peculiar operations of the Civil War. Similarly, the action off Lissa led to a cult of the ram which has left a deep impress upon shipbuilding, while a few isolated successes obtained by torpedoes, in exceptional circumstances, have given rise to exaggerated claims on behalf of this weapon which can only end in disappointment. Instances could be multiplied, and the obvious moral is the vital necessity for the most careful study by the clearest available brains before translating any so-called lesson of war into national policy. In a single year a navy of the magnitude of our own may be committed to many millions of expenditure, the result of which will affect its fighting efficiency for nearly a quarter of a century. The vital need for caution and for profound study of all such experience as is forthcoming is, therefore, evident. The battle of Tsu-shima is by far the greatest and the most important naval event since Trafalgar, and the navy which is able to draw the most accurate conclusions, technical as well as tactical, from its experiences and to apply them in terms of policy and of training will secure marked advantage in the future.