The Saar Offensive was the French invasion of Saarland, Germany, in the first stages of World War II, from 7 to 16 September 1939. The original plans called for 40 divisions, and one armored division, three mechanised divisions, 78 artillery regiments and 40 tank battalions to assist Poland, which was then under invasion, by attacking Germany's neglected western front. Despite 30 divisions advancing to the border (and in some cases across it), the attack did not have the expected result. When the swift victory in Poland allowed Germany to reinforce its lines with homecoming troops, the offensive was halted. French forces then withdrew amid a German counter-offensive on 17 October. Background In 1921, the French Army and the Polish Army made a defensive alliance against Germany in their military convention. Objective of the offensive According to the 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 defences. The sector was defended by the German 1st Army. 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 pre-emptive mobilisation was started in France on 26 August and on 1 September, full mobilisation was declared. French mobilisation suffered from an inherently out of date system, which greatly affected their ability to swiftly deploy their forces on the field. The French command still believed in the tactics of World War I, which relied heavily on stationary artillery, even though this took time to transport and deploy. Many pieces also had to be retrieved from storage before any advance could be made. French operations Almost everyone expected a major French attack on the Western Front soon after the start of the war, but Britain and France were cautious as both feared large German air attacks on their cities; they did not know that 90 per cent of German frontline aircraft were in Poland. A French offensive in the Rhine valley began on 7 September, four days after France declared war on Germany. The Wehrmacht was engaged in the attack on Poland and the French enjoyed a decisive numerical advantage along the border with Germany but the French did not take any action that was able to assist