Ireland. Jubilant at this news, he ordered General Moltke, the German chief of staff, to "march the whole of the... army to the East". This allegedly brought Moltke to the verge of a nervous breakdown, who protested that "it cannot be done. The deployment of millions cannot be improvised." Lichnowsky soon realised he was mistaken, although Wilhelm insisted on waiting for a telegram from his cousin George V; once received it confirmed there had been a misunderstanding, and he told Moltke "Now do what you want." Aware of German plans to attack through Belgium, French Commander-in-Chief Joseph Joffre asked his government for permission to cross the border and pre-empt such a move. To avoid a violation of Belgian neutrality, he was told any advance could come only after a German invasion. On 2 August, Germany occupied Luxembourg and exchanged fire with French units; on 3August, they declared war on France and demanded free passage across Belgium, which was refused. Early on the morning of 4August, the Germans invaded and Albert I of Belgium called for assistance under the Treaty of London. Britain sent Germany an ultimatum demanding they withdraw from Belgium; when this expired at midnight without a response, the two empires were at war. Progress of the war Opening hostilities Confusion among the Central Powers The strategy of the Central Powers suffered from miscommunication. Germany had promised to support Austria-Hungary's invasion of Serbia, but interpretations of what this meant differed. Previously tested deployment plans had been replaced early in 1914, but those had never been tested in exercises. Austro-Hungarian leaders believed Germany would cover its northern flank against Russia. Germany, however, envisioned Austria-Hungary directing most of its troops against Russia, while Germany dealt with France. This confusion forced the Austro-Hungarian Army to divide its forces between the Russian and Serbian fronts. Serbian campaign Beginning on 12 August, the Austrian and Serbs clashed at the battles of the Cer and Kolubara; over the next two weeks, Austrian attacks were repulsed with heavy losses, dashing their hopes of a swift victory and marking the first major Allied victories of the war. As a result, Austria had to keep sizeable forces on the Serbian front, weakening its efforts against Russia. Serbia's defeat of the 1914 invasion has been called one of the major upset victories of the twentieth century. In spring 1915, the campaign saw the first use of anti-aircraft warfare after