The modem was created in the context of a US strategic automatic air defense network to transmit data from radar stations over large distances over the existing telephone system. A significant early challenge was how to minimize noise, which was conceptualized in terms of echo effects, impulse noise, and phase distortion. The approaches to solving the noise problem varied with the techniques of modulation and demodulation used by early modems. The problem of minimizing noise was crucial to the development of the modem, and the focus the military placed on automatic air defense spawned decades of work into the further refinement of modem technology.