The Battle of Køge Bay on july lst 1677, in which Admiral Niels Juel gained an overwhelrning victory over the Swedish fleet, was of particular importance for Denmark, not only strategically but also for its bearing on the fleet's own personnel. 

Since we do not possess Niels Juel's own report of the battle, the description of the sequence of events during the battle has had to be founded on other sources, and several of the episodes during the battle have been the object of discussion. On the basis of the report of the Swedish Admiral Horn together with Danish log books and reports, it has been maintained that before the battle the preliminary manoueuvres had taken place on an east-westerly course between Falsterbo and Stevns. While making her way to Stevns and Køge Bay the Swedish vessel the Dragon went aground near Sierslev on Stevns, and it has been disputed as to whether Niels Juel himself took part in combatting the Dragon. The following proofs of Niels Juel's participation have been brought to light, however: a letter from the master of the Dragon, Rear-Admiral Taube, the paying out of prize money, and the interrogation of the farmers who helped in the boarding of the ship. Taube mentions "the Admiral himself", and Niels Juel declares in a letter that Taube would surrender to none other than himself. The prize for the conquest of the Dragon was awarded to Niels Juel alone and, at the inquiry, direct mention was made of Niels Juel's secretary on board the Dragon. 

Yet another problem connected with the paying out of the prize money was the fact that the money was paid out not only to the crew of Niels Juel's flagship, the Christianus Quintus, but also to the crew of the Fridericus Tertius. Since we know that Niels Juel did in fact change flagships, this change must have taken place here at Stevns. This is further substantiated by the fact that the Fridericus Tertius was in the squadron which had dropped out of line during the previous night and, approaching from the north, had joined up with the fleet again just below Stevns. The reason why the change of flagship took place here and not later during the battle was because precisely this squadron had been assigned to tackle the Dragon's escorts, and even though it met up with the fleet later on this renewed attachment to the Danish fleet took place while the battle was going on and part of the Swedish fleet lay between Niels Juel and the squadron concerned. 

The grounding of the Dragon caused a certain amount of confusion in the Swedish fleet, so that when the Swedes eventually withdrew to the Baltic, Niels Juel saw his opportunity to cut through the Swedish lines and cut off some of the ships, after which the last phase of the battle became a vessel-to-vessel skirmish. During the preceding years Niels Juel had trained his masters in this kind of breakthrough technique, and had carried it out successfully in 1676 during a battle with a Swedish fleet of greater striking power. The success of this breakthrough in the battle of Køge Bay was among other things due to the change in wind direction that took place during the course of the day. The opposing fleets lay on a south-easterly course from Stevns and, when the wind turned towards the west, by hauling to the wind, Niels Juel was able to sail straight through a gap in the Swedish lines. The ships that were cut off thus came under double fire, since they were attacked also from the north by the Danish squadrons which had previously attacked the Dragon's escorts. 

During the skirmishes that followed, the Admiral's ship again suffered a severe attack, and Niels Juel had to change flagships once more, this time transferring his flag to the Charlotta Amalia. The first change of ship soon became known in Copenhagen and was mentioned, among other things, in a letter from the Admiral of the Realm, whose knowledge of the change of flagship sprung from that fact that the Christianus Quintus was left behind at Stevns to be towed to Copenhagen and repaired. The other change did not become known before Niels Juel returned from his pursuit of the Swedish fleet. This too shows clearly that some time elapsed between the two events, though this did not come to light in the rather superficial accounts in the newspapers of that time, the so-called "relations". Apart from that, the news of Niels Juel's breakthrough was reported fairly early on, because another ship - the Norwegian Lion, had witnessed it but had had to withdraw from the fight on account of the damages received during these skirmishes.

Niels Juel could not catch up with the faster Swedish vessels when they fled to the Baltic and, on reaching Bornholm, he turned homewards again with his fleet, though was prevented by a head wind from reaching Køge Bay again before July 4th. Of the Swedish vessels which had escorted the Dragon, some fled to the Baltic while others made for Malmø. These latter were attacked and conquered the following day by the supporting Dutch fleet which had entered the Sound on July lst. The sea battle was also instrumental in showing that the Danish fleet could manage without the help of the Dutch.