The Iron Gate I hydropower and navigation system (km 943+600 of the Danube) was commissioned on 6 August 1970. Each power plant, Serbian and Romanian of the same size, includes six power units with Kaplan turbines of 190 MW nominal power per unit. During the design and construction phases, these were the largest units of the kind in the world. In the 21st century the Iron Gate I HPP will still represent the focal point of the power supply systems of Serbia and Romania, as well as the focal point of navigation on the Danube with its navigation channels falling within the framework of development of European Corridor VII. After the onset of operation (1970-1972), the power units have on the average been subjected to about 200,000 hours of operation each. The calculated operating life of the equipment has elapsed, and testing shows clear signs of ageing. In order to avoid operation with increased frequency of failure and downtime, resulting in significant production losses and increased maintenance costs, as well as to prevent possible damage, it is necessary to refurbish the power units and vital ancillary equipment in a timely fashion.