<P> The first day on the Somme (1 July) saw a serious defeat for the German Second Army, which was forced out of its first position by the French Sixth Army, from Foucaucourt - en - Santerre south of the Somme to Maricourt on the north bank and by the Fourth Army from Maricourt to the vicinity of the Albert--Bapaume road . The first day on the Somme was, in terms of casualties, also the worst day in the history of the British army, which suffered 57,470 casualties . These occurred mainly on the front between the Albert--Bapaume road and Gommecourt, where the attack was defeated and few British troops reached the German front line . The British troops on the Somme comprised a mixture of the remains of the pre-war regular army; the Territorial Force; and Kitchener's Army, a force of volunteer recruits including many Pals' Battalions, recruited from the same places and occupations . </P> <P> The battle is notable for the importance of air power and the first use of the tank . At the end of the battle, British and French forces had penetrated 10 km (6 mi) into German - occupied territory, taking more ground than in any of their offensives since the Battle of the Marne in 1914 . The Anglo - French armies failed to capture Péronne and halted 5 km (3 mi) from Bapaume, where the German armies maintained their positions over the winter . British attacks in the Ancre valley resumed in January 1917 and forced the Germans into local withdrawals to reserve lines in February, before the scheduled retirement to the Siegfriedstellung (Hindenburg Line) began in March . Debate continues over the necessity, significance and effect of the battle . David Frum opined that a century later, "' the Somme' remains the most harrowing place - name" in the history of the British Commonwealth . </P> <P> Allied war strategy for 1916 was decided at the Chantilly Conference from 6--8 December 1915 . Simultaneous offensives on the Eastern Front by the Russian army, on the Italian Front by the Italian army, and on the Western Front by the Franco - British armies, were to be carried out to deny time for the Central Powers to move troops between fronts during lulls . In December 1915, General Sir Douglas Haig replaced Field Marshal Sir John French as Commander - in - Chief of the BEF . Haig favoured a British offensive in Flanders close to BEF supply routes, to drive the Germans from the Belgian coast and end the U-boat threat from Belgian waters . Haig was not formally subordinate to Marshal Joseph Joffre but the British played a lesser role on the Western Front and complied with French strategy . In January 1916, Joffre had agreed to the BEF making its main effort in Flanders, but in February 1916 it was decided to mount a combined offensive where the French and British armies met, astride the Somme River in Picardy before the British offensive in Flanders . A week later the Germans began an offensive against the French at Verdun . The costly defence of Verdun forced the French army to commit divisions intended for the Somme offensive, eventually reducing the French contribution to 13 divisions in the Sixth Army, against 20 British divisions . By 31 May, the ambitious Franco - British plan for a decisive victory, had been reduced to a limited offensive to relieve pressure on the French at Verdun with a battle of attrition on the Somme . </P> <P> The Chief of the German General Staff, Erich von Falkenhayn, intended to end the war by splitting the Anglo - French Entente in 1916, before its material superiority became unbeatable . Falkenhayn planned to defeat the large amount of reserves which the Entente could move into the path of a breakthrough, by threatening a sensitive point close to the existing front line and provoking the French into counter-attacking German positions . Falkenhayn chose to attack towards Verdun to take the Meuse heights and make Verdun untenable . The French would have to conduct a counter-offensive on ground dominated by the German army and ringed with masses of heavy artillery, leading to huge losses and bring the French army close to collapse . The British would then have to begin a hasty relief offensive and would also suffer huge losses . Falkenhayn expected the relief offensive to fall south of Arras against the Sixth Army and be destroyed . (Despite the certainty by mid-June of an Anglo - French attack on the Somme against the Second Army, Falkenhayn sent only four divisions, keeping eight in the western strategic reserve . No divisions were moved from the Sixth Army, despite it holding a shorter line with ​ 17 ⁄ divisions and three of the reserve divisions in the Sixth Army area . The maintenance of the strength of the Sixth Army, at the expense of the Second Army on the Somme, indicated that Falkenhayn intended the counter-offensive against the British to be made north of the Somme front, once the British offensive had been shattered .) If such Franco - British defeats were not enough, Germany would attack the remnants of both armies and end the western alliance for good . The unexpected length of the Verdun offensive, and the need to replace many exhausted units at Verdun, depleted the German strategic reserve placed behind the Sixth Army, which held the Western Front from Hannescamps, 18 km (11 mi) south - west of Arras to St. Eloi, south of Ypres and reduced the German counter-offensive strategy north of the Somme, to one of passive and unyielding defence . </P>

British generals in the battle of the somme