Motivated by patriotism, Sassoon joined the British Army just as the threat of a new European war was recognized, and was in Service with the Sussex Yeomanry on 4 August 1914, the day the United Kingdom of Great Britain and Ireland declared war on Germany. He broke his arm badly in a riding accident and was put out of action before even leaving England, spending the spring of 1915 convalescing. (Rupert Brooke, whom Sassoon had briefly met, died in April on the way to Gallipoli.) He was commissioned into the 3rd Battalion (Special Reserve), Royal Welch Fusiliers, as a second lieutenant on 29 May 1915. On 1 November his younger brother Hamo was killed in the Gallipoli Campaign, and in the same month Siegfried was sent to the 1st Battalion in France. There he met Robert Graves, and they became close friends. United by their poetic vocation, they often read and discussed each other's work. Though this did not have much perceptible influence on Graves's poetry, his views on what may be called 'gritty realism' profoundly affected Sassoon's concept of what constituted poetry. He soon became horrified by the realities of war, and the tone of his writing changed completely: where his early poems exhibit a Romantic, dilettantish sweetness, his war poetry moves to an increasingly discordant music, intended to convey the ugly truths of the trenches to an audience hitherto lulled by patriotic propaganda. Details such as rotting corpses, mangled limbs, filth, cowardice and suicide are all trademarks of his work at this time, and this philosophy of 'no truth unfitting' had a significant effect on the movement towards Modernist poetry.