In early June 1757, the French army began to advance towards Hanover once it became clear that there was to be no negotiated agreement. The first skirmish between the two forces had taken place on 3 May. Part of the French army was delayed by the Siege of Geldern which took three months to capture from its Prussian garrison of 800. The bulk of the French army advanced across the Rhine, advancing slowly because of the difficulties of logistics for moving an army estimated at around 100,000.
In the face of this advance, the smaller German Army of Observation retreated back across the River Weser into the territory of the Electorate of Hanover itself, while Cumberland tried to ready his troops. On July 2,the Prussian port of Emden fell to the French before a Royal Navy squadron sent to relieve it could reach there. This cut Hanover off from the Dutch Republic meaning that supplies from Britain could now only be shipped direct by sea. The French followed this up by seizing Cassel, securing their right flank.