After the German invasion into the Netherlands, German navy was much interested in the Dutch harbours. First they began to build fortresses that had only a temporal character. Later it became clear they couldn't invade in England, and coastal defences became more permanent. At the same time, the Allies began to bombard certain areas systematically. The German navy would give construction of coastal batteries the highest priority. Along the coast they created "widerstandsneste", which were linked to groups of bases on the other hand, along the entire coast, groups of bases that filled an important task in the defence, were linked to fortresses. In this way the " Fortress IJmuiden " originated in IJmuiden. This fortress had a large autonomy and should be equipped so that it could withstand also long siege. Besides the mobile defence, tank-defence-guns, panzer and light armed infantry, they build light shelters. They also built strongly executed defence-facilities, with enormous amounts of concrete.
To the defence of the coastal-batteries, they built Flak batteries (defence of air raids). At the country-front, obstacles were erected and field guns stationed at strategically important strongholds. In the fortress IJmuiden, they had built some Flak batteries. Battery Olmen is still free accessible, all emplacements can be visited. With this " home page ", I try to describe what they could find on a Flakbatterie. It isn't complete and any information is welcome.