Napoleon owed much of his success to masterly use of artillery. Under this captain there was no preparation for infantry advance by slowly disintegrating the hostile force with artillery fire. Rather, his artillerymen went up fast into closest range, and by actually annihilating a portion of the enemy line with case-shot fire, covered the assault so effectively that columns of cavalry and infantry reached the gap without striking a blow! After Napoleon, the history of artillery largely becomes a record of its technical effectiveness, together with improvements or changes in putting well-established principles into action. UNITED STATES GUNS OF THE EARLY 1800's The United States adopted the Gribeauval system of artillery carriages in 1809, just about the time it was becoming obsolete (the French abandoned it in 1829). The change to this system, however, did not include adoption of the French gun calibers. Early in the century cast iron replaced bronze as a gunmetal, a move pushed by the growing United States iron industry; and not until 1836 was bronze readopted in this country for mobile cannon. In the meantime, U. S. Artillery in the War of 1812 did most of its fighting with iron 6-pounders. Fort McHenry, which is administered by the National Park Service as a national monument and historic shrine, has a few ordnance pieces of the period. [Illustration: Figure 10--U. S. 32-POUNDER ON BARBETTE CARRIAGE (1860).] During the Mexican War, the artillery carried 6- and 12-pounder guns, the 12-pounder mountain howitzer (a light piece of 220 pounds which had been added for the Indian campaigns), a 12-pounder field howitzer (788 pounds), the 24- and 32-pounder howitzers, and 8- and 10-inch mortars. For siege, garrison, and seacoast there were pieces of 16 types, ranging from a 1-pounder to the giant 10-inch Columbiad of 7-1/2 tons. In 1857, the United States adopted the 12-pounder Napoleon gun-howitzer, a bronze smoothbore designed by Napoleon III, and this muzzle-loader remained standard in the army until the 1880's. The naval ironclads, which were usually armed with powerful 11- or 15-inch smoothbores, were a revolutionary development in mid-century. They were low-hulled, armored, steam vessels, with one or two revolving turrets. Although most cannonballs bounced from the armor, lack of speed made the "cheese box on a raft" vulnerable, and poor visibility through the turret slots was a serious handicap in battle. [Illustration: Figure 11--U. S. NAVY 9-INCH SHELL-GUN ON MARSILLY CARRIAGE (1866).]