The key characteristic of modern machine guns, their relatively high rate of fire and more importantly machine (automatic) loading, came with the Model 1862 Gatling gun, which was adopted by the United States Navy. These weapons were still powered by hand; however, this changed with Hiram Maxim's idea of harnessing recoil energy to power reloading in his Maxim machine gun. Dr. Gatling also experimented with electric-motor-powered models; this externally powered machine reloading has seen use in modern weapons as well. The Vandenburg and Miltrailleuse volley (organ) gun concepts have been revived partially in the early 21st century in the form of electronically controlled, multibarreled volley guns. In Machine Guns: A Pictorial, Tactical, and Practical History author Jim Thompson offers useful information on machine guns and how they actually function in the field, enough history for you to understand how and why the guns were developed, and advice about the machine gun's best friend and worst enemy, ammunition. Detailing the models by country of development, Thompson includes weapons from the World War I era through today, and provides hundreds of photographs and illustrations.