The submarine was located in the Belgian exclusive economic zone (EEZ), the area up to 200 nautical miles (more than 370 kilometers) from the coast. It was the patrol vessel Castor that did the monitoring.
According to VRT, the submarine entered Belgian waters at 9 a.m. and crossed the border with the Netherlands at 1 p.m. It is said to be a damaged submarine. The navy points out that Belgian patrol vessels monitor the North Sea day and night.