 Iron ships had first been proposed for military use in the 1820s . In the 1830s and 1840s , France , Britain and the United States had all experimented with iron @-@ hulled but unarmored gunboats and frigates . However , the iron @-@ hulled frigate was abandoned by the end of the 1840s , because iron hulls were more vulnerable to solid shot ; iron was more brittle than wood , and iron frames more likely to fall out of shape than wood . 
 Iron ships <a href='been_done' title='1'><mark>had</mark></a> first been proposed for military use in the 1820s . In the 1830s and 1840s , France , Britain and the United States <a href='been_done' title='2'><mark>had</mark></a> all experimented with iron @-@ hulled but unarmored gunboats and frigates . However , the iron @-@ hulled frigate was abandoned by the end of the 1840s , because iron hulls <a href='uninflect' title='3'><mark>were</mark></a> more vulnerable to solid shot ; iron was more brittle than wood , and iron frames more likely to fall out of shape than wood . 
Iron ships done first been proposed for military use in the 1820s . In da 1830s and 1840s , France , Britain and the United States done alll experimented with iron @-@ hulled but unarmored gunboats and frigates . However , the iron @-@ hulled frigate was abandoned by the end of the 1840s , because iron hulls was more vulnerable to solid shot ; iron was more brittle than wood , and iron frames more likely to fall outt of shape den wood .