11. The French invented a new type of floating battery
To press the attack at Gibraltar French engineers developed a new type of floating battery, with hulls three feet thick, filled with sand and lined on the outside with heavy cable to deaden incoming shot. The batteries were equipped with pumps to keep the sides constantly wet as a countermeasure against fire. Only one side of the battery was equipped with guns, the opposite side was also filled with sand to counterbalance the weight. The batteries were to be used close inshore, to pound British gun emplacements supported by fire from the Spanish siege works. French engineers built ten of the floating batteries, which were supported by the ships of the line in the harbor, nearly fifty ships armed with heavy guns.
As it became evident that the peace commissioners in Paris were nearing an agreement which would end the war between France and Great Britain, recognizing American independence, the Spanish moved forward with greater urgency towards the reduction of the British outpost of Gibraltar. It was in the long term strategic interests of the French to ensure that the gateway to the Mediterranean was in the hands of the Bourbon King of Spain, and the French commitment to seizure of Gibraltar remained steady, despite the cession of hostilities in the North American theater. In September 1782, French and Spanish commanders decided to overwhelm the defenders with a massive bombardment, followed by an assault by troops from both the floating batteries and the Spanish siege lines.