For SSKs energy storage is crucial; since the time being completely submerged – thus not having the need to snorkel – is essential to keep the operational advance of being stealthy. Air independent propulsion (AIP) systems today are state of the art while most submarine builders do not have mature systems operational; almost all are working on fuel cell systems. thyssenkrupp Marine Systems having supplied most AIP submarines that are operational based on fuel cells (FC) has developed a fourth generation of fuel cells. Compared to previous systems the new system features latest FC technology, thus improving operational availability, cost and independence of suppliers. T In addition, batteries are the traditional energy storage for SSKs. Having used lead-acid batteries for over 100 years, a technology change is under way. Lithium Ion batteries offer higher capacity, more power, faster charging and a longer lifetime. The paper will show the special requirements of the submarine application and the technical solutions, which are now ready for use on board of submarines.