_Merrimack’s_ reincarnation as _Virginia_ embodied two technologies—steam and iron (and then steel)—that were advanced during the Civil War and that eventually defined the modern Navy. Steam engineering had traveled a long road of acceptance in the conservative Navy. By 1850, the year the Charlestown Navy Yard built its first steamer, Great Britain had built or converted from sail some 25 propeller and paddlewheel steam warships. The U.S. Navy had launched only seven. Steam engines were still considered novelties by many old Navy men—at best auxiliary power, at worst dirty and undependable nuisances that called for machine tenders rather than sailors. Their resistance was not entirely unjustified. There was the problem of range: _Merrimack_, for instance, could cruise only about 17 days with its coal bunker full. American steamers far from home had to depend on French or British coaling stations and machine shops in places like Hong Kong and Shanghai. Unlike self-reliant sail, steam alone could not meet the demands of distant squadrons. And in the early days of steam, it was no faster than sail: in fact it was often slower. More crucial, early steam engines were inefficient and unreliable, so captains would not trust them in combat. And coal took up valuable space needed for supplies, crew, and ammunition. But the main problem was that early steamers were driven by big, ungainly sidewheels that caused captains no end of problems (_see page 35_). They so harmed a vessel’s sailing qualities that steam was of necessity the primary power source on sidewheelers—but the Navy wanted to use steam only as auxiliary power. Another way of employing steam power for propulsion was needed. The propeller (called a “screw”) was the answer, allowing naval steam to come into its own. Construction of the prototype screw sloop _Princeton_ began in 1841, before America’s first sidewheel warships even went into service. The Navy built only eight more deepwater sidewheelers before the famous 1854 class of six screw steamers (led by the Charlestown-built _Merrimack_) made the cumbersome vessels a footnote in naval history. With the advent of the propeller, enough problems were solved that auxiliary steam power became feasible in warships. On an 1858 cruise from Honolulu to Acapulco, _Merrimack_ steamed only three days out of 32. _Merrimack_, whose subsequent adventures we have already followed, was in the tradition of large American frigates like _Constitution_. While its engines were never very dependable, _Merrimack_ was an excellent sailer, powerfully armed, and on its inaugural European cruise inspired Britain to build similar vessels with better engines. [Illustration: Merrimack _is launched at Charlestown in 1855;_ Cumberland _was built in the same shiphouse in 1842_.]