...had left Venice isolated, though the city…

...had left Venice isolated, though the city continues to resist recapture by enemy forces until August.

The earliest recorded use of an unmanned aerial vehicle in combat occurs on August 22, 1849, when the Austrians attack Venice with unmanned balloons loaded with explosives.

At least some of the balloons are launched from the Austrian ship Vulcano.

Although some of the balloons work, others are caught in a change of wind and blown back over Austrian lines.

The Austrians had been developing this system for months: "The Presse, of Vienna, Austria, has the following: 'Venice is to be bombarded by balloons, as the lagoons prevent the approaching of artillery. Five balloons, each twenty-three feet in diameter, are in construction at Treviso. In a favorable wind the balloons will be launched and directed as near to Venice as possible, and on their being brought to vertical positions over the town, they will be fired by electro magnetism by means of a long isolated copper wire with a large galvanic battery placed on a building. The bomb falls perpendicularly, and explodes on reaching the ground.'" (Scientific American, March 1849)

Although balloons do not generally meet today's definition of a unmanned aerial vehicle, or UAV, the concept is strong enough that once winged aircraft are invented, the effort to fly them unmanned for military purposes will not be far behind.