Underwater acoustic communication is a technique of sending and receiving message below water. There are several ways of employing such communication but the most common is using hydrophones. A hydrophone is a microphone designed to be used underwater for recording or listening to underwater sound. Multiple hydrophones can be arranged in an array so that it will add the signals from the desired direction while subtracting signals from other directions. In this paper we study the gain brought by hydrophone array on underwater acoustic communications.