34 years ago today, on 4 December 1990, Danish Tumleren-class submarine HDMS Sælen (S323) sank while being towed from Copenhagen to Aarhus. On 17 December, she was raised by the German floating crane Roland and taken to Aarhus for repair. On 10 August 1993, diving approval was issued and the boat was recommissioned.
Now a museum ship at Skibene på Holmen, Copenhagen, Denmark.