the end of the era. Machine guns were valued for their ability to smash infantry formations, especially attacking enemy formations when they were dense. This, along with effective field artillery, changed tactics drastically. Static defense Static defenses evolved from the use of permanent fortifications that were direct descendants of medieval castles. As artillery improved in destructive power and penetrative ability, more modern fortifications were developed, using first thicker layers of stone, then concrete and steel. After naval artillery developed the turret – a moving cannon platform – land fortifications started to use this method as well. Between the World Wars, France built an "impregnable" underground steel and concrete fortification that ran the length of the German-French border. This Maginot Line failed to stop German tanks in 1940: they bypassed the fortifications by invading through neighboring Belgium. Temporary fortifications As artillery and rifles allowed the killing of enemy personnel at a longer effective range, soldiers started to dig into temporary fortifications. These included massive trenches as used in WWI, and individual soldier-sized "fox holes" which became more common in WWII. Maneuver warfare Maneuver had existed throughout military history – from soldiers marching on the field to using horses in cavalry formations. It was not until the advent of mechanized transport over unprepared terrain, such as fields and deserts, using tanks and armored vehicles, that "maneuver warfare" became feasible. First used by the German army in Poland and France in WWII, Blitzkrieg or "lightning war" saw whole armies moved rapidly on tracked and armored fighting vehicles. During the war airborne movement was used, with soldiers dropped to the battlefield by parachute by both the Germans and the Allies. After WWII, developments in helicopters brought a more practical way to transport troops by air. Armoured warfare Blitzkrieg Deep operations Naval warfare Ironclads and Dreadnoughts The period after the Napoleonic Wars was one of intensive experimentation with new technology; steam power for ships appeared in the 1810s, improved metallurgy and machining technique produced larger and deadlier guns, and the development of explosive shells, capable of demolishing a wooden ship at a single blow, in turn required the addition of iron armor, which led to ironclads. The famous battle of the CSS Virginia and USS Monitor in the American Civil War was the duel of ironclads that symbolized the changing times. Although the battle was inconclusive, nations around the world subsequently raced to convert their