DoD has a critical need to increase the reliability, range and expanse of acoustic undersea communications with manned and unmanned platforms and distributed sensing systems. The highly variable nature of the ocean environment results in complex propagation paths for acoustic signals. Various factors including propagation delay, time-varying multipath and fading, natural and man-made noise, Doppler shift, low-bandwidth and energy constraints make undersea communications and networking extremely challenging. Innovative methods are needed to increase the reliability, range and expanse of undersea acoustic communications throughout large ocean basins. To address this, IAI will develop a Sensor Expanded Acoustic-Undersea Reliable Configurable Heterogeneous Integrated Network (SEA-URCHIN) system, which introduces advanced physical layer algorithms to conventional underwater communications modems. Moreover, IAI will implement MAC and network protocol stacks in order to transmit the sensor information to the information center in a timely manner while accounting for sensor battery constraints. Further, IAI will develop models for the algorithms and use IAI’s state-of–the-art underwater communications simulator to study the performance of the system. Once the algorithms are refined and the simulation results meet the performance goals, IAI will move on to hardware implementation, and conduct field tests of the SEA-URCHIN system. This effort will decrease the operational cost of the sensor deployment for underwater networks. The developed mobile node routing algorithms and SDR acoustic modems will be highly valuable for search and rescue, geo-sciences and underwater exploration efforts. It will have military applications in undersea communications with manned and unmanned platforms and distributed sensing systems, as well as commercial applications in undersea communications to support research, mining, and infrastructure monitoring and development.