The NACS is a state-of-the-art system to determine the in-situ performance of sonar systems. NACS comprises of four sub-systems: a linear stave of transducers, electronics, a computer, and software for computations and control of the system. It is interfaced with the sonar system. The NACS stave is fitted inside the sonar dome and is only a few centimeters away from the sonar array. At the heart of this system are theoretical models of the near and far-field acoustic radiation from an array of transducers and the response of the array to near and far-field sources of sound.