Modern warfare is warfare that is in notable contrast with previous military concepts, methods, and technology, emphasizing how combatants must modernize to preserve their battle worthiness. As such, it is an evolving subject, seen differently in different times and places. In its narrowest sense, it is merely a synonym for contemporary warfare. In its widest sense, it includes all warfare since the "gunpowder revolution" that marks the start of early modern warfare, but other landmark military developments have been used instead, including the emphasis of artillery marked by the Crimean War, the military reliance on railways beginning with the American Civil War, the launch of the first dreadnought in 1905, or the use of the machine gun, aircraft, tank, or radio in World War I. In other senses, it is tied to the introduction of total war, industrial warfare, mechanized warfare, nuclear warfare, counter-insurgency, or (more recently) the rise of asymmetric warfare also known as fourth-generation warfare. Types Some argue that the changing forms of third generation warfare represents nothing more than an evolution of earlier technology. Aerial Aerial warfare is the use of military aircraft and other flying machines in warfare. Aerial warfare includes bombers attacking enemy concentrations or strategic targets; fighter aircraft battling for control of airspace; attack aircraft engaging in close air support against ground targets; naval aviation flying against sea and nearby land targets; gliders, helicopters and other aircraft to carry airborne forces such as paratroopers; aerial refueling tankers to extend operation time or range; and military transport aircraft to move cargo and personnel. Asymmetric A military situation in which two belligerents of unequal strength interact and take advantage of their respective strengths and weaknesses. This interaction often involves strategies and tactics outside conventional warfare. Biological Biological warfare, also known as germ warfare, is the use of any organism (bacteria, virus or other disease-causing organism) or toxin found in nature, as a weapon of war. It is meant to incapacitate or kill enemy combatants. It may also be defined as the employment of biological agents to produce casualties in man or animals and damage to plants or material; or defense against such employment. Biological warfare involves the intentional release of living pathogens either in their naturally occurring form, for example the diseased corpses of animals, or in the form of specific human-modified organisms. Chemical Chemical warfare is warfare (associated military operations) using the toxic properties of