The Ultimate Weapon

The Ultimate Weapon is a 1936 science fiction novel by American writer John W. Campbell  initially published under the title of Uncertainy as a series in  Amazing Stories in October and December editions in 1936.

Plot
Alien invaders escape their doomed home-planet of Mira and bring their starship fleet to conquer Earth. Nothing stands in the way of the Miran invaders, except Buck Kendall, who has discovered the ultimate weapon that is Earth's last hope.