Passage: Ostfriesland and her three sisters were to have taken part in a final fleet action at the end of October 1918, just over 2 weeks before the Armistice was signed. The bulk of the High Seas Fleet was to have sortied from its base in Wilhelmshaven to engage the British Grand Fleet; Scheer—by now the Großadmiral (Grand Admiral) of the fleet—intended to inflict as much damage as possible on the British navy, to improve Germany's bargaining position, despite the expected casualties. But many of the war-weary sailors felt that the operation would disrupt the peace process and prolong the war. On the morning of 29 October 1918, the order was given to sail from Wilhelmshaven the following day. Starting on the night of the 29th, sailors on Thüringen and then on several other battleships mutinied. The unrest ultimately forced Hipper and Scheer to cancel the operation. Informed of the situation, the Kaiser stated "I no longer have a navy". On 16 December, Ostfriesland was decommissioned and used as a barracks ship.

Question: When was Ostfriesland decommissioned?
16 December