The Ultimate Weapon by John W. Campbell, Science Fiction, Adventure 12+

🔖 RED SUN RISINGThe star Mira was unpredictably variable. Sometimes it was blazing, brilliant and hot. Other times it was oddly dim, cool, shedding little warmth on its many planets. Gresth Gkae, leader of the Mirans, was seeking a better star, one to which his "people" could migrate. That star had to be steady, reliable, with a good planetary system. And in his astronomical searching, he found Sol.And on Earth there was nothing which would be capable of beating off this incredible armada-until Buck Kendall stumbled upon THE ULTIMATE WEAPON.