I mentioned to a friend that I was writing a book on the physics so war. "What does physics have to do with war? he asked. "Oh, you mean the atomic bomb," he added. And indeed most people know that physics had something to do with the atomic bomb. But in reality it has made many contributions  other than the atomic bomb, and not all of them have led to the creation of offensive weapons that have caused damage and grief. It has also been helpful for defense, and one of the best examples is the invention of radar just before II. It saves thousands of lives during the Battle of Britain. The discovery of X-rays has played a large role in war, and there's no doubt that it has saved lives. The book that I wrote is called "The Physics of War: From Arrows to Atoms," and it traces the use of physics and science in general in warfare from the beginning of history. In a  sense it's a history of the world, since war has played such an important role in our history. The use of the bow and arrow in early wars is discussed along with the discovery of gunpowder and its use in early cannons. The contributions of Leonardo da Vinci, Galileo, Newton, Einstein and many others is discussed. And finally, the Napoleonic wars, the American civil war, world war I and II, and the making of the atomic bomb are all discussed.