In the early years of the 20th century the military aeroplane was a frail structure of wood, wire, and fabric. It was intended as an aid to reconnaissance and was capable of carrying little in the way of defensive armament; it flew at a maximum speed of less than 120 km/h (74 mph). Aircraft could not carry any really useful armament until 1915. Attempts to carry one machine-gun severely affected the performance of the aircraft, which only had low-powered engines. Three guns were not feasible until late 1917, and then only on two-seater aircraft, such as the Bristol F2b Fighter-the problem being one of a lack of power and the vibration set up by the guns firing. In 1914, the aircraft could barely carry one machine-gun and then at the expense of altitude performance. Only when engines became more powerful did the machine-gun replace the rifle.
In the 80 years since World War I began, the military aeroplane has evolved into a sophisticated weapons system of enormous complexity. Specialized aircraft fulfil a variety of roles, from reconnaissance and interception to air superiority and strategic bombing. Jet-powered aircraft can travel at up to three times the speed of sound, carrying an arsenal of weapons, including nuclear devices each capable of destroying an entire city.
The aircraft has continuously revolutionized the conduct of warfare throughout the century. From the first experiments with aircraft as observation platforms directing artillery fire, through the invention of aerial bombardment and the consequent need for air defence, to World War II's strategic bombing offensive and eventually nuclear deterrence, air power has dictated the conduct of 20th-century war. Air power has provided military commanders with new means of gathering intelligence, dominating a battlefield, striking the enemy over great distances, and forging global lines of supply and communication. For the first time, aviation made civilians at home as vulnerable to attack as soldiers on the battlefield.