 The ironclad age saw the development of explosive torpedoes as naval weapons , which helped <unk> the design and tactics of ironclad fleets . The first torpedoes were static mines , used extensively in the American Civil War . That conflict also saw the development of the spar torpedo , an explosive charge pushed against the hull of a warship by a small boat . For the first time , a large warship faced a serious threat from a smaller one — and given the relative <unk> of <unk> against ironclads , the threat from the spar torpedo was taken seriously . The U.S. Navy converted four of its monitors to become <unk> armored spar @-@ torpedo vessels while under construction in 1864 – 5 , but these vessels never saw action . Another proposal , the towed or ' Harvey ' torpedo , involved an explosive on a line or <unk> ; either to deter a ship from <unk> or to make a torpedo attack by a boat less <unk> . 
