Hello eggie,
the source of information is my visit there; you may find this address also on the internet, e.g. 'https://www.defensie.nl/onderwerpen/t/thuisfront/praktisch/vertrek-en-aankomst' . You could use a search engine either, looking for 'Rijkszee- en Marinehaven 1'. According to my local colleagues, the whole area uses this address. That is why i pointed out the main gate. It would have helped me if I would have known this in advance, but this adress was unknown to OSM.
Kind regards, U02
OpenStreetMap