During the 250 years immediately preceding 1830, the navies of the world did not greatly change in their material composition and in the technical requirements of their personnel. If Drake's men had found themselves in Nelson's Victory, they would, without prolonged training, have sailed and fought her with considerable efficiency. During these centuries, therefore, the development of matériel and personnel need not constantly engage the historian's attention. On the other hand, the use of navies as instruments of national policy, and the consequent campaigns waged at sea, loom too large to be disregarded.

After 1830, however, the emphasis is exactly reversed. Now the great seafaring nations are no longer in endemic conflict, and the nations most usually at war are not the seafaring nations. So ‘operations’ fall naturally into the background, and, though fleets are still used as instruments of policy, that use is more indirect, less primarily warlike. There now occurs, however, a series of unparalleled revolutions in matériel which, extending inevitably to personnel, profoundly alters the whole nature of navies. Though Nelson's men could have gone back two-and-a-half centuries without trouble, they would have been utterly bemused if called upon to go forward only a quarter of that period.

It is, therefore, the great evolutions in the ships themselves, their propulsion, weapons and equipment, and in their men which must be the main concern here. It is in the period from 1830 to 1870, indeed, that those changes were at their quickest and most bewildering, and in their results most decisive. The navies of 1830 were still, in essence, the navies of Nelson and Villeneuve: those of 1870 were already, in most respects, those of Fisher and von Tirpitz.