O 9-class submarine

The O 9 class was a class of three submarines, built for the Royal Netherlands Navy. Used for patrols in the Dutch home waters. The class comprised O 9, O 10, and O 11. The submarines diving depth was 60 meters.

Construction
The ships were built by three different shipyards. O 9 was built by the Koninklijke Maatschappij De Schelde in Flushing. O 10 in Amsterdam at the Nederlandsche Dok en Scheepsbouw Maatschappij and O 11 in Rotterdam at Fijenoord shipyard.

At the time of the German invasion O 11 was under repair in Den Helder. On 14 May 1940 she was scuttled there to prevent her being captured by German forces. However the Germans raise the ship and order its repair. In September 1944 O 11 is sunk in Den Helder to block the entrance of the harbour.