This invention is a composite acoustic lens that can be steered internally through electrical control. It can collect and direct acoustic energy from a plane wave to focus it on a transducer. It can also take the nearly omnidirectional output from a standard acoustic transducer and direct its energy in a plane wave. In the receive role the lens increases the effective signal-to-noise ratio of the array; in the transmit role it reduces the output energy that is responsible for reverberation. The lens is steerable by virtue of its material: it is electrorheological. Its bulk modulus, and the resulting speed of sound, can be changed electrically. Controlling the gradient of the index of refraction allows the steering to be adjusted precisely, continuously, and quickly. It is held by a container of plastic material that matches the acoustic impedance of water and minimizes the presence of near-field scatterers. A system based on the proposed lens can improve the effectiveness of both active and passive sonars, reduce the detectability of active transmissions and reduce the inboard footprint. Medical applications exist for both imaging and lithotriptic devices.