September 7 in Swedish History
1631: the Battle of Breitenfeld takes place, approximately five miles northwest of the walled city of Leipzig, Germany. It is the Protestants’ first major victory in the Thirty Years War, and it means the German states will not be forcibly reconverted to Roman Catholicism.
The victory also shows Sweden’s Gustav II Adolf as a great tactical leader and it induces many Protestant German states to ally with Sweden against the German Catholic League, led by Maximilian I, Elector of Bavaria, and the Holy Roman Emperor Ferdinand II of Austria.
The King had entered the Thirty Year's War in earnest a little over a year earlier on the anti-Imperial side, which at the time was losing to the Holy Roman Empire and its Catholic allies. The Swedish forces would reverse that situation.

Gustav II Adolf was leading the Swedish army on the European continent beginning with the Polish-Swedish War (1625–1629), where he fought against his cousin Sigismund III of Poland, who wanted to regain the throne of Sweden.
The King was therefore not present in Stockholm for the maiden voyage of the Swedish warship Vasa, which foundered and sank after sailing less than a nautical mile. We just passed the anniversary of the discovery of the shipwreck by Anders Franzén on August 26: Swedish marine technician and amateur naval archaeologist Anders Franzen (1918-1993) discovers the warship Vasa (Read Nordstjernan reporting from the final salvage five years later on the same page)