The ROK Navy found defects in the cables of the inverter module, one of the central components in the propulsion system, aboard ROKS Son Won-il, ROKS Yoon Bong-gil, and ROKS Yoo Gwan-soon. These are the first, fifth, and sixth boats of the class. Each submarine will have to go through a complex overhaul to receive repairs. This will immobilize each vessel at least four months.
To make matters worse, the inverter modules, produced by Siemens, cannot be fixed in Korean shipyards due to legal barriers concerning technology transfers and intellectual property. Therefore, the parts will need to be shipped to Germany for repairs, with the round way trip expected to last 2 months, leading to each submarine being out of action for at least 6 months.