Warmatrix

A helicopter is the most common type of rotorcraft that can lift off and land vertically, without the need for an airstrip. It is a versatile aircraft that is used for reconnaissance, troop and weapon transport, as a rescue vehicle, submarine hunter and flying artillery.
People have been playing with rotorcraft since ancient times. The named 'helicopter' was coined by Gustave de Ponton d'Amécourt. In 1861 CE, he and two other engineers designed a kind of airship with many rotorblades. It could not take off because its steam engine was too heavy for the power that it generated. During the Second Industrial Revolution the internal combustion engine became available and engineers started to develop helicopters that used it. It was a difficult process that took about four decades. Finally, in 1936 CE, Heinrich Focke built the Focke-Wulf FA-61, the world's first practical transverse twin-rotor helicopter. Six years later Igor Sikorsky developed the R-4, using a main rotor and a small tail rotor, a design that would become the most common among helicopters. In the course of three years, 131 R-4's were built; the age of the helicopter had begun.
Helicopters saw little action during World War II. Development continued and armies all over the world slowly started to adopt them. During the Korean War they proved effective in dealing with the rugged terrain, acting as scouts and suppliers, and evacuating wounded soldiers. In 1951 CE the Kaman K-225 was the first helicopter powered by a turbine engine. The increased power allowed for higher speeds and heavier payloads, greatly increasing helicopter usability. From the 1960's CE onward almost all armies and some navies employ helicopters.
The successes of early helicopters prompted military strategists to think about other uses for them. They came up with a kind of 'sky cavalry', in which helicopters provide the high mobility that used to be an attribute of traditional horse cavalry. The close connection with ground forces is the main reason why helicopters, though they are aircraft, ended up as part of armies and navies, not air forces.
Despite all their advantages, helicopters have their limits. For one, their payload is limited: it ranges from a just few tons to the 25 tons of the Russian Mi-26M. Because they fly relatively low and slow, they are vulnerable to even small anti-aircraft fire and attacks by airplanes, though they can sometimes duck below radar or hide behind hills and mountains. Therefore they are at their best against enemies with weak air defenses, such as guerrillas who operate in rugged terrain. An example of this is their success in the Vietnam War.
Infantry deployed ahead of the traditional frontlines found themselves in need of fire support. This lead to the development of attack helicopters, designed to attack ground targets. These act like flying artillery. Subsequent development has transformed many of them into independent attackers, who engage without infantry.