The first electronic digital computer used in a real-time application and the first to use magnetic core memory. The Whirlwind was originally intended to be a general-purpose aircraft simulator for the U.S. Navy, but evolved into a general-purpose computer that became the prototype for the SAGE air defense system (see SAGE). Developed at the Massachusetts Institute of Technology, construction began in 1947. It became operational in the early 1950s.

Its first memory used electrostatic storage tubes that proved unreliable, and in 1953, magnetic core memory was added, dramatically improving performance and reliability. The Whirlwind used 2K words of core memory and magnetic drum and tape for storage. The machine was continually enhanced, eventually using 12,000 vacuum tubes and 20,000 diodes and occupying two floors of an MIT campus building.

Whirlwind's circuit design, core memory and use of CRTs contributed greatly in the making of future computers. Project members later worked on IBM's 700 series. One in particular, Kenneth Olsen, founded Digital Equipment Corporation.