On 28 July 1914, the First World War began. On 4 August, Germany invaded Belgium, and the United Kingdom entered the war against the German Empire. The same day, reservists were called-up and ordered to join the division to bring it up to full strength. The war establishment of each of the BEF's divisions was 18,179 men. This process took until 9 August. Three days later, the majority of the division embarked ships at Southampton and began landing at Le Havre the following day. By 21 August, the division had fully arrived in France and had assembled on the Belgian border along with the rest of the BEF.