War came, but even then the full possibilities of shell fire were not developed. Enough proof was given, however, to show that in the special circumstances of that war unarmoured ships were of small value against shell fire. Armour was accordingly requisitioned, and, some few years after the war, was applied to seagoing warships. Another development now took place. At this period when disruptive and incendiary shell was proving itself a more powerful agent than solid shot of equal size, both shell and shot gained an enhanced value from the application of rifling to ordnance; moreover, ordnance itself was developing so quickly that each year saw an appreciable increase in the unit of artillery force. This variation in the unit profoundly affected naval architecture. No longer was there a unit of standard and unchanging value, which, when multiplied by a certain number, conveyed a measure of a ship’s offensive power. No longer was the size of a ship a rough measure of its fighting strength; by concentrating power in a few guns, offensive strength could be correspondingly concentrated, if desired, in a small vessel. On the other hand, in view of the sudden accession of offensive strength, the defensive capacities of a ship remaining as before, it was now true that size had become an element of danger, diminutiveness of safety. Hence warships, which had for centuries triumphed in the moral and physical effect of their height and size, suddenly sought to shrink, to render themselves inconspicuous, to take the first step towards total invisibility. An effect of the same development--of the increasing size of the unit gun, and therefore of the decreasing number of units which a ship could carry--was the mounting of every big gun so as to command as large an arc of fire as possible. As the final development we note that the steam engine, in endowing the warship with motions far more variable, certain and controlled than those of the sailing ship, called forth tactical ideas quite different, in many respects, from those which governed sea actions in the canvas period. The warship itself is the embodiment of tactical ideas. Hence the design of the steam-propelled warship evolved along a different line from that of the sailing ship. By the effect and interaction of these developments a complete revolution was compassed in naval architecture; by the progress of artillery and the steam engine, and by the improvement in mechanical processes in general, an entirely new unit of naval force was evolved from the old sailing ship: the mastless, turreted ironclad of the late ’sixties, the precursor of the modern battleship. §