In 1865 the United States possessed a fleet fully able to protect the whole line of its immense sea-coast against foreign aggression; in 1870 the fleet was reduced to a handful of vessels that, whilst showing heterogeneousness equal to the English fleet, did not possess a single element of strength. At the date of the outbreak of the Crimean war, the building of sailing war-vessels may be said to have ceased throughout the world. Steam corvettes and frigates formed the bulk of the effective fighting fleets, whilst steam line-of-battle ships were being slowly introduced, as yet scarcely beyond the experimental stage. The introduction of steam propulsion and the advancement in the science of naval architecture had given rise not only to improvements in design, strength, and seaworthiness of men-of-war, but also to a gradual increase in dimensions of the different classes. The extent of this advancement is well shown in comparing the English line-of-battle ship Victory, Nelson’s flag-ship at Trafalgar, having a displacement of less than 2900 tons, with the _average_ displacement of English first-class frigates in 1854, which was not less than 2800 tons; the battery power of the frigates being more than twice as effective, steam-power being added, and handiness and speed under sail alone being much superior. Progress in this direction had been made to the extent that in 1854 the French had laid the keel of the Imperatrice Eugènie, a frigate of 3600 tons displacement, designed for a speed of 12 knots and a battery of 56 guns (five and six inch smooth-bores). At the declaration of war with Russia neither the English nor the French navy was in a condition to meet the suddenly created exigencies; both fleets were in a transition state from sail to steam. The necessity for steam-power on all ships was suddenly made forcibly apparent, and architectural development ceased almost entirely in the work of converting all the available line-ships and frigates of the old sailing fleet into steamers.