FOI has done research in acoustic underwater communication, concerning both algorithm development, implementation and networks. The research has mainly been financed by FoT (defense research and technical development). In this report 2010 year's work is described from a technical aspect. The first subject is spread-spectrum communication and its use in the underwater context. It is clear that there is not any decisive reason to use spread-spectrum except from when you whish to obtain a stealth signal, i.e. low spectrum density in the signal. In the report a method that gives a real signal processing gain is described and which therefore is better to use. In next chapter a motivation is given to our choice to use a single-carrier modulation in stead of OFDM, as many others have chosen. The reason for our choice is that the richness of multi-path in the channel can be used to make the communication more robust, without the need for a return channel from the transmitter to the receiver. We also report some ways to improve or circumvent errors in the phase tracking of the signal to be decoded. In the end of chap. three, some results from an experiment outside of Elba in Italy are given. The result of the research has given opportunities to more secure speech and data communication under the water surface. The research is now mature to enter into an phase of industrialization. We also describe a new underwater modem that has been developed by FOI. This will give rise to new safety equipment for submarines and effectivisation of the marine defense by increasing the possibilities for cooperation and to use of new sensors. The report is concluded with discussions around some scenarios which have been developed within the Racun project.