According to the Franco-Polish military convention, the French Army was to start preparations for the major offensive three days after mobilisation started. The French forces were to effectively gain control over the area between the French border and the Siegfried Line and were to probe the German defenses. On the 15th day of the mobilization (that is on 16 September), the French Army was to start a full-scale assault on Germany. The preemptive mobilization was started in France on 26 August and on 1 September full mobilization was declared.