DoE is seeking low-cost, user-friendly monitoring tools for Marine and Hydrokinetic (MHK) energy sites. It is looking for novel, low-cost methods for environmental monitoring and resource characterization. Shipboard monitoring is expensive, fixed monitoring sites and drifters are inflexible, and there are no affordable, easily deployable single-source solutions to monitor above and below water, near and far. SubSeaSails mission is to develop 100% energy harvesting, disruptively-affordable, long-duration maritime platforms and sensors. SSS surface vessels are available today but the development of a submerging capability will provide enhanced monitoring by being able to listen, measure and monitor at depths. Measuring and monitoring underwater has significant advantages. For example, sound travels long-distances underwater but listening at the surface is complicated by natural (weather/waves/wind) and human-created noise so utilizing passive acoustic arrays at 10+ meters is advantageous. Likewise, the use of sensors such as magnetometers will benefit by underwater proximity. In Phase I, SSS will design a submerging vessel and identify sensors to be integrated to measure and monitor at levels down to 30 meters. It will also create a prototype that can demonstrate the submerging capability in a demonstration facility (e.g. a tank) or in the ocean. Since pressure increases about one atmosphere for every 10 meters of water depth, SSS will design how to harden the vessel, find and integrate high-capability sensors that are small (size and weight), low current draw and have appropriate depth rating that can be utilized on the vessel above and below water. The ability to autonomously provide near and far field monitoring from a 100% renewable energy vessel that can sail to locations, maintain position, submerge for periods of time to listen/measure/monitor, return to the surface to monitor while re-charging batteries, transmit data, and remain at sea for extended periods will be unique and a fraction of the cost of other systems. In Phase II, SSS will design and build a functioning prototype vessel that can submerge and measure/monitor down to 100 meters. Given the pressures and time underwater that vessel will endure and likely long mission duration periods, it will be a larger vessel than current SSS surface models. Clean, renewable, ocean energy is a massive global opportunity. Wherever installations are put in the ocean there needs to be good environmental monitoring before, during and after installation. There is a global need for the type of affordable monitoring that SSS is proposing. The development of clean, consistent offshore renewable energy is an extraordinary opportunity to promote a sustainable Clean Economy while promoting a sustainable Blue Economy. This proposal is for the development of 100% energy harvesting, submerging vessels that can monitor before, during and after installation that can be built in the U.S. and exported to support offshore developments globally.