In December 1674 a Swedish army came south out of Swedish Pomerania into the March of Brandenburg and found almost nothing in its way. The Elector's soldiers were hundreds of kilometres off in Franconia, fighting the French as part of the Imperial army in the Franco-Dutch War, and the country they had left behind could not defend itself. The Swedes spent the winter and spring living off it. Not until June 1675 did the Brandenburg army turn around and march home, and what it managed then was a forced march hard enough to leave the troops spent when they arrived. The speed mattered more than the numbers. The Elector's whole plan depended on getting there before the Swedes understood he had got there at all.

Swedish Field Marshal Carl Gustav Wrangel's intention was to move from Havelberg across the Elbe, gain the left bank, link up with Hanoverian troops and push on Magdeburg. To secure the river line he sent a detachment forward under Colonel Wangelin to Rathenow. On 15 June Field Marshal Georg von Derfflinger talked his way in. Speaking fluent Swedish, he presented himself at the Havel Gate as an officer fleeing the Brandenburgers, the drawbridge came down, and his dragoons were inside the town before the garrison understood what had happened. Wangelin was taken prisoner. The coup undid the entire Swedish scheme at a stroke — with Rathenow gone, the Elbe crossing at Havelberg was out of reach. Lieutenant General Wolmar Wrangel issued fresh orders: the army would fall back through Nauen and secure the crossing of the Rhin at Fehrbellin instead. The Elector set off after them immediately. From that moment the campaign was no longer a manoeuvre. It was a chase.

Lieutenant Colonel Sydow's twelve hundred horsemen reached the ground in front of Nauen first, which is why the abandoned guns went into the water. The Brandenburg cavalry chased the retreating Swedes to the edge of the town and cut them down as they ran — most of the men who died at Nauen died in flight, not in a stand-up fight, which is how these things usually went and is worth saying plainly. Inside the town a battalion of Swedish musketeers made a real stand, meeting the advance with heavy musket and cannon fire. Even before the Brandenburg guns and dragoons came up, two hundred troopers pushed back a rearguard of a thousand cuirassiers. The Swedes gave up Nauen and withdrew, taking further casualties as they went.

Beyond the town ran a stream, and at the far end of its bridge the Swedes had built a battery. That was where the Brandenburg pursuit stopped. The guns drove the cavalry back with losses, and behind the works the main Swedish army had drawn up in order of battle. Field Marshal Georg von Derfflinger got the damaged bridge repaired and three cannon into position, and his gunners knocked out the Swedish pieces — but the enemy line was still solid, and a frontal assault across a single bridge against a deployed army was more than the Elector was willing to buy. His own men had been in the saddle or on the road for days. The order went out to pull back into Nauen and camp. Roughly two hundred Swedish soldiers had been killed in and around the town; about sixty Brandenburgers.

By the evening of 17 June the two armies were close enough to hear one another, and the Brandenburg camp expected to fight at first light in front of the gates of Nauen. The Swedes had other plans. They used the darkness to break contact and slip away northwest toward Fehrbellin. The Elector's army broke camp at half past five the next morning and went after them, and on 18 June 1675 caught them at the Rhin crossing. Fehrbellin is the battle the history books remember; it is the day Frederick William became the Great Elector, and the day a middling north German state began to be taken seriously as a military power. But Fehrbellin only happened because a Swedish army was already retreating, already short of guns, and already a day behind. That was decided at Nauen.