The idea of warfare conducted from an aerial ship was proposed as early as 1670 by the Italian Jesuit Francesco de Lana Terzi in his book of inventions Prodromo overo saggio di alcune invenzioni nuove. A balloon was first used for military purposes in 1794, during the French revolution, when French army observers stationed in a balloon directed ground fire against Austrian forces. Contemporary engravings illustrate another military application: a fanciful proposal to employ balloons as troop transports to invade England. In 1862 and 1863, during the American Civil War, the Army of the Potomac used balloons to observe Confederate movements. A balloon sent to Cuba during the Spanish-American War was used to direct U.S. artillery fire at the Battle of San Juan.