In 1906 Lee de Forest patents the Audion, the first triode: a three-electrode vacuum tube capable of amplifying weak electrical signals. The triode makes commercial radio, long-distance telephony, radar, and early electronic computers (ENIAC, 1946, used ~18,000 vacuum tubes) possible. Fragile and power-hungry, it is the direct technological precursor the transistor (1947) was explicitly designed to replace.