Underwater networks are envisioned to enable several applications for oceanographic data collection, environmental monitoring, navigation, and tactical surveillance. Underwater acoustic networking is the enabling technology for these applications. Most of these applications make use of underwater vehicles and rely on inter-vehicle communication capabilities for information exchange and coordination purposes. Reliable data delivery, especially in the case of mobile underwater vehicles, is therefore a major concern in many of these applications. In this paper, three versions of a reliable unicast protocol are proposed, which integrate MAC and routing functionalities and leverage different levels of neighbor knowledge for making optimum decisions for reliable data delivery. The different levels of neighbor knowledge used by the protocols are: (i) no neighbor knowledge, (ii) one-hop neighbor knowledge, and (iii) two-hop neighbor knowledge. The three versions of the protocol have been devised by considering the peculiar characteristics of underwater channel, in design as well as in performance simulation. The protocols have been compared in static as well as mobile scenarios in terms of different end-to-end networking metrics.