Jay Forrester and Robert Everett, working for the United States Navy, completed the construction of ' Whirlwind,' a 'real-time computer,' taking twice the space of ENIAC, which could constantly monitor its inputs, making it suitable for simulations.  In the course of its development, Forrester devised 'magnetic-core memory.'  Whirlwind's success caused the U. S. Air Force to fund Project Lincoln, which used Whirlwind as the test bed for the air defense system.  This system required analog-digital tele-communication and its engineers built a device called a modulator-demodulator, or 'modem.'