Modern underwater acoustic (UWA) modems, besides receiving-transmitting data, can measure signal propagation time and evaluate the distance between the transmit-ter and the receiver. Such capabilities can be exploited for synchronization of UWA sensor networks, where sensing and actuation must be coordinated across multiple nodes, UWA positioning and navigation of autonomous underwater vehicles. How-ever, such problem as the accuracy of propagation time measurement, especially in highly reverberant environment, as well as the evaluation of clock skew on interact-ing modems, have been investigated rather poorly. One of the objectives consists in experimental evaluation of the precision of propagation time measurements between UWA modems communicating in reverberant environments (Fig.5), as well as in demonstration of the modems built-in tools providing opportunities for precise esti-mation of the modems clock skews (Fig.6). Another objective is to demonstrate a “comfortable” way for clock synchronization of UWA network nodes directly during payload data exchange (Fig.1). Experiments were carried out during CommsNet13 sea trials, CMRE, La Spezia.