The Saar Offensive was a French attack into the Saarland defended by the German 1st Army in the early stages of World War II. Its purpose was to assist Poland, which was then under attack. The assault was stopped after a few kilometres and the French forces withdrew. According to the Franco-Polish military convention, the French Army was to start preparations for a major offensive three days after the beginning of mobilisation. The French forces were to effectively gain control over the area between the French border and the German lines and were to probe the German defences. On the 15th day of the mobilisation (that is on 16 September), the French Army was to start a full-scale assault on Germany. The preemptive mobilisation was started in France on 26 August, and on 1 September full mobilisation was declared.