A more practical and influential weapon was the self @-@ propelled or Whitehead torpedo . Invented in 1868 and deployed in the 1870s , the Whitehead torpedo formed part of the armament of ironclads of the 1880s like HMS Inflexible and the Italian Caio Duilio and Enrico Dandolo . The ironclad 's vulnerability to the torpedo was a key part of the critique of armored warships made by the Jeune Ecole school of naval thought ; it appeared that any ship armored enough to prevent destruction by gunfire would be slow enough to be easily caught by torpedo . In practice , however , the Jeune Ecole was only briefly influential and the torpedo formed part of the confusing mixture of weapons possessed by ironclads .