This report summarizes the activities within the underwater communications project during 2015-2017. A large portion of these efforts (>90%) is connected to three international collaborations and a strategical national effort. The three international collaborations treat Communications links at low transmission levels, communication solutions for wireless underwater sensor networks, and adaptive solutions for underwater networking. In order to obtain effective solutions for underwater communications, all these complement each other in a good manner. In addition to this, the project has also contributed to a large national project in autonomous underwater robots. The high data rate methods that FOI has developed and tested in sea trials during several years are quite mature by now. They have been designed primarily for transfer of digital speech and target data in near real time between ships and submarines. Throughout the project, a number of new methods for acoustic underwater communications have been developed. They have been designed to cope with difficult situations, i.e. when the underwater channel does not permit high data rates because of too much time- and Doppler spreading. Common for these new methods is robustness and limited complexity. In addition, network protocol solutions for underwater sensor networks have been developed and analysed. The report concludes with a summary and also recommendations of what should be focused on ahead.