The American Civil War was probably the first truly modern war in that technology was so important. The military use of balloons, the development of steam-powered ironclads and monitors (as well as the invention of the gun turret), rifled cannons of unprecedented size, submarines, guncotton and telegraphy were all invented or perfected during the war. brought about great advances in the use of technology in warfare. The only thing that was missing was heavier-than-air flight.
In 1862, an architectural engineer named William C. Powers sought to correct that omission. Living in Mobile, Alabama, Powers was acutely aware of the devastating effect of the Union blockade of southern ports. With the Union holding the upper hand in the strength of its navy, Powers decided that if it were impossible to break through the blockade it might be possible to fly over it. And not just fly over it—destroy it in the process.
Powers drew up detailed plans for a machine that could support itself in the air by purely mechanical means. This would give it a commanding advantage over the balloon—which had been used already to great effect by the Union as a aerial observation platform. Thaddeus Lowe's balloons were invariably tethered, if not they would have been subject to every vagary of the wind and weather. They made great places from which to observe a battle but if you wanted to travel in a specific direction at a specific speed you were out of luck if the wind wasn't going your way.
Balloons also had a disadvantage in that they were limited in the amount of payload they could carry—without having recourse to impossibly gigantic balloons.
Powers may have been aware of the work on helicopters already being done in Europe and some aspects of Powers' design would seem to suggest that he was. For instance, the "steam air liner" of Gabrielle de la Landelle. On the other hand, he seemed to have eschewed the propellers that the European inventors were tending toward and looked back 400 years to the air screw devised by Leonardo Da Vinci.
Like many of the Europeans, Powers' craft was to have been powered by a steam engine (de la Landelle, in collaboration with Gustave Ponton Amecourt, had developed a working steam engine for a model helicopter in 1861—it's possible that Powers was aware of this). Located in the middle of the fuselage, it drove two enormous Archimedean screws that provided lift and two screws mounted on either side of the hull to that provided thrust. A large rear-mounted rudder allowed the craft to be steered.
Powers was certainly aware of da Vinci's helicopter, but he wasn't the first to suggest the Archimedean screw as a method for driving an airship. Powers may have also known of the work of inventors such as Pierre Ferrand, who in 1835 proposed a dirigible in which the cylindrical gas bag was one giant rotating screw.
Powers' drawings show that he intended the air frame of his helicopter to have a lattice-like cellular construction. This would have provided great strength at the same time saving weight. This was a method reinvented 80 years later and used in the construction of bombers during World War II.
Although Powers constructed a non-flying model, his plans to build a full-scale version never came to pass. Lack of funds was one obvious reason and the other is that he apparently feared that should it fall into the hands of the Union, it would be replicated in mass and used to rain death and destruction upon southern armies and cities.
In spite of Powers' secrecy regarding his invention, one does wonder if Lu Senarens, the teenage author of the Frank Reade, Jr. series of dime novels, might not have gotten wind of it...