The measurement capability of a 2.5‐m‐diam anechoic steel tank for calibrating underwater electroacoustic transducers has been considerably increased by the installation of a nearfield transducer array. Because the boundary conditions required for valid measurements with the array are less restrictive than those that apply without the array, both the size of transducers and the frequency range of measurement are greater than was permissible formerly. Design criteria for the array are given. Data gathered from two years experience are presented to show the array's performance at 7 MPa (1000 psi) hydrostatic pressure and at the temperatures 3° and 25°C.