many exhausted units at Verdun, depleted the German strategic reserve placed behind the Sixth Army, which held the Western Front from Hannescamps, 18 kilometres (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.
Battle of Verdun
The Battle of Verdun (21 February–18 December 1916) began a week after Joffre and Haig agreed to mount an offensive on the Somme. The German offensive at Verdun was intended to threaten the capture of the city and induce the French to fight an attritional battle, in which German advantages of terrain and firepower would cause the French disproportionate casualties. The battle changed the nature of the offensive on the Somme, as French divisions were diverted to Verdun, and the main effort by the French diminished to a supporting attack for the British. German overestimation of the cost of Verdun to the French contributed to the concentration of German infantry and guns on the north bank of the Somme. By May, Joffre and Haig had changed their expectations of an offensive on the Somme, from a decisive battle to a hope that it would relieve Verdun and keep German divisions in France, which would assist the Russian armies conducting the Brusilov Offensive. The German offensive at Verdun was suspended in July, and troops, guns, and ammunition were transferred to Picardy, leading to a similar transfer of the French Tenth Army to the Somme front. Later in the year, the Franco-British were able to attack on the Somme and at Verdun sequentially and the French recovered much of the ground lost on the east bank of the Meuse in October and December.
The Brusilov Offensive (4 June–20 September), absorbed the extra forces that had been requested on 2 June by General von Below, the Second Army commander, for a spoiling attack on the Somme. On 4 June, Russian armies attacked on a 200-mile (320 km) front, from the Rumanian frontier to Pinsk and eventually advanced 150 kilometres (93 mi), reaching the foothills of the Carpathian mountains, against German and Austro-Hungarian troops of Armeegruppe von Linsingen and Armeegruppe Archduke Joseph. During the offensive the Russians inflicted c. 1,500,000 losses including c. 407,000 prisoners. Three divisions were ordered from France to the Eastern Front on 9 June and the spoiling attack on the Somme was abandoned. Only four more divisions were sent to the Somme front before the Anglo-French offensive began, bringing the total to 10 1⁄2 divisions. Falkenhayn, and then Hindenburg and Ludendorff, were forced to send divisions to Russia throughout the summer to prevent a collapse of the Austro-Hungarian army and then to conduct a counter-offensive against Romania, which declared war against the Central Powers on 27 August. In July there were 112 German divisions on the Western Front and 52 divisions in Russia and in November there were 121 divisions in the west and 76 divisions in the east.
The original British Expeditionary Force (BEF) of six divisions and the Cavalry Division, had lost most of the army's pre-war regular soldiers in the battles of 1914 and 1915. The bulk of the army was made up of volunteers of the Territorial Force and Kitchener's New Army, which had begun forming in August 1914. Rapid expansion created many vacancies for senior commands and specialist functions, which led to many appointments of retired officers and inexperienced newcomers. In 1914, Haig had been a Lieutenant-General in command of I Corps and was promoted to command the First Army in early 1915 and then the BEF in December, which eventually comprised five armies with sixty divisions. The swift increase in the size of the army reduced the average level of experience within it and created an acute equipment shortage. Many officers resorted to directive command, to avoid delegating to novice subordinates, although divisional commanders were given great latitude in training and planning for the attack of 1 July, since the heterogeneous nature of the 1916 army, made it impossib