War was declared with Mexico on May 12, 1846. The share of the navy in the occupancy of the east coast of the country, apart from its landing a very efficient battery of heavy guns at Vera Cruz, which assisted materially in a quick surrender of the place, was not of very great importance beyond occupying all the other towns of the coast, a duty in every case gallantly performed. The importance of naval action in the Pacific was far different, for it secured to us California, then a part of Mexico. Whatever the later official statements as to British intent, or non-intent, it was well that our ships were on the ground first and in possession; in any case our action on the California coast forestalled any question. There was from the treaty of peace with Mexico, February 2, 1848, to our next and greatest war, an interval of but thirteen years. This was one of the periods of greatest transition in which the ships and guns which had existed for over two hundred years with but moderate change were to take a long step to complete transformation, from sail to steam, and from the smooth-bore to the rifle. In the matter of guns, though, we were much slower to change than was Europe. We were to carry aboard our ships, during the Civil War and for long after, the smooth-bore Dahlgren gun, so called from the bottlelike form given it by the inventor, Commander (later Rear-Admiral) J. A. Dahlgren. One by one, or at most by occasional twos, the new-fangled idea--the steamship--had made its way. In 1837 had been built the _Fulton_, of 4 guns; in 1841, the _Missouri_, which was to perish by fire at Gibraltar but two years later, 1843; and the _Mississippi_, a sister ship, which after many years of honorable service was to find her grave in the river of her name at Port Hudson on March 14, 1863; in 1843 was built our first screw steamer, the _Princeton_; in 1844 at Erie our first iron steamer, the _Michigan_, for service on the lakes, where she cruised for many years and became in lapse of time a curiosity; in 1848, the _Saranac_; and in 1850 the two fine old side-wheel frigates, the _Susquehanna_ and the _Powhatan_. By 1855 we were building the five frigates, _Wabash_, _Roanoke_, _Colorado_, _Merrimac_, and _Minnesota_, the finest of their time, but which except the _Merrimac_, transformed into an ironclad, were to cut no figure in the coming Civil War on account of their deep draft. Their time had passed even by 1861. CHAPTER XXI