(1905) Sir John Ambrose Fleming made the first diode tube, the Fleming valve. The device had three leads, two for the heater/cathode and the other for the plate.
(1907) Lee De Forest added a grid electrode to Fleming’s’ valve and created a triode, later improved and called the Audion.
(1921) Albert W. Hull, an American engineer, invented a vacuum tube oscillator called it a magnetron. The magnetron was the first device that could efficiently produce microwaves. Radar, which was developed gradually during the 1920's and 1930's, provided the first widespread use of microwaves.
The introduction of Vacuum tubes at the beginning of the 20th century was the starting point of the rapid growth of modern electronics. With vacuum tubes manipulation of signals because possible, which could not be done with the early telegraph and telephone circuit or with early transmitters using high voltage sparks to create radio waves. For example, with vacuum tubes weak radio and audio signals could be amplified, and audio signals, such as music or voice, could be superimposed on radio waves. The development of a large variety of tubes designed for specialized functions made possible the swift progress of radio communication technology before World War II.
The vacuum tube era reached its peak with the completion of the first general purpose electronic digital computer in 1945. This huge machine, called ENIAC (Electronic Numerical Integrator and Computer) was built by the two engineers at the University of Pennsylvania,
J. Presper Eckert, Jr., and John W. Mauchly. The computer
contained about 18,000 vacuum tubes and occupied about 1,800 square feet of
floor space. ENIAC worked 1000 times faster than the fastest non electronic
computers then in use.