Despite having no other connection to the university, in 1912 Slim joined the Birmingham University Officers' Training Corps, and he was thus able to be commissioned as a temporary second lieutenant into the Royal Warwickshire Regiment on 22 August 1914, on the outbreak of the First World War; in later life, as a result of his modest social origins and his unpretentious manner, he was sometimes wrongly supposed to have risen from the ranks. He was badly wounded at Gallipoli. On return to England, he was granted a regular commission as a second lieutenant in the West India Regiment.