As already suggested, the necessity for armor arose from the smashing and splintering effect of shell against wooden targets and the penetrating power of rifled guns. To attack Russian forts in the Crimea, the French navy in 1855 built three steam-driven floating batteries, the _Tonnant, Lave_, and _Devastation_, each protected by 4.3-inch plates and mounting 8 56-lb. guns. In the reduction of the Kinburn batteries, in October of the same year, these boats suffered little, but were helped out by an overwhelming fire from wooden ships, 630 guns against 81 in the forts. The French armored ship _Gloire_ of 1859 caused England serious worry about her naval supremacy, and led at once to H. M. S. _Warrior_, like the _Gloire_, full rigged with auxiliary steam. The _Warrior's_ 4.5-inch armor, extending from 6 feet below the waterline to 16 feet above and covering about 42 per cent of the visible target, was proof against the weapons of the time. At this initial stage in armored construction, naval experts turned with intense interest to watch the work of ironclads against ships and forts in the American Civil War. _The American Civil War_ The naval activities of this war are too manifold to follow in detail. For four years the Union navy was kept constantly occupied with the tasks of blockading over 3000 miles of coast-line, running down enemy commerce destroyers, cooperating with the army in the capture of coast strongholds, and opening the Mississippi and other waterways leading into the heart of the Confederacy. To make the blockade effective and cut off the South from the rest of the world, the Federal Government unhesitatingly applied the doctrine of "continuous voyage," seizing and condemning neutral ships even when bound from England to Bermuda or the Bahamas, if their cargo was ultimately destined for Southern ports. The doctrine was declared inapplicable when the last leg of the journey was by land,[1] doubtless because there was little danger of heavy traffic across the Mexican frontier. Blockade runners continued to pour goods into the South until the fall of Fort Fisher in 1865; but as the blockade became more stringent, it crippled the finances of the Confederacy, shut out foodstuffs and munitions, and shortened, if it did not even have a decisive effect in winning the war. [Footnote 1: Peterhoff Case, 1866 (5 Wall, 28).]