As the world becomes more aware of the opportunities and issues posed by Unmanned Air Systems, the question arises as to what the impact of other unmanned systems are. Frazer-Nash Consultancy on behalf of the UK Defence Science and Technology Laboratory (Dstl) has taken an independent view of Unmanned Underwater Systems (UUS), both now and up to 20 years in the future. We have developed an evidence-based projection of the capability of UUSs through a structured and systematic approach considering the functional decomposition into subsystems of: sensing, energy, processing, navigation, communication, propulsion, artificial intelligence, manipulation, launch and recovery. Nearly 70 technologies were considered for their impact including biological fuel cells, new battery technologies, quantum processing and sensing, soft robotics and self-healing systems. Utilising information in the public domain and engaging with UUS stakeholders, we have isolated trends in technology maturity and performance to understand historic developments. We have then projected these into the future, considering if fundamental physical limits will be reached or how development in nanotechnology, biotechnology and novel materials will affect development. These projections show the high-likelihood development in capability which we would expect to see. To capture the potential of disruptive technology breakthroughs, we also considered low-likelihood, high-impact developments, to ensure that the projections were not impeded by a lack of imagination. In summary, the results consider the rate of change of development in subsystems as well as disruptive application opportunities. The results show that a significant number of technologies are technically feasible within the next 2-5 years, but that it is likely to be much longer before they are commercially available. The greatest areas of growth are in sensing and processing. We have developed artist’s impressions of potential UUS concepts applying new technologies arising over 3 epochs of time: 2-5 years, 5-10 years and 10-20 years.