Plans for a joint Anglo-French offensive around the River Somme in the summer of 1916 were first discussed at the Allied conference at Chantilly in December 1915. With rumours abounding that Germany was running out of reserves, the Allied generals were confident that an attack on the 40-mile front to the north and south of the river would provide the long-awaited breakthrough in the West.

However, the plan for a combined operation was blocked by the German bombardment of the French fortress of Verdun, which began in February 1916 and lasted the rest of the year. Large parts of the French army were caught up in this bloody rearguard action. The Somme offensive became a predominantly British operation, in the hands of the commander-in-chief of the British army in France, Douglas Haig, and the head of the Fourth Army, Henry Rawlinson.

Despite their experience of fighting on the Western Front, Haig and Robertson showed little wisdom in their planning and execution of the Somme attack. The strategy of limited attacks using rapidly moving and well-protected infantry was abandoned in favour of an attack over a 20-mile area, in which the infantry proceeded towards enemy lines in slow, rigid formations that provided easy targets for German machine-guns. As both private and operational sources illustrate, the first day of the battle, 1 July 1916, was a bloody failure: 20,000 of the 120,000 men who attacked were killed. The territorial gains bought by this sacrifice were minimal.

The disastrous first-day offensive did not shake Haig's belief that a series of similar assaults would lead to Germany's capitulation. But between 2 July and the end of August, the British gained little more ground than they had done on 1 July at the cost of 82,000 further casualties.

Prospects brightened briefly in September 1916, when new artillery techniques and the first deployment of tanks in battle helped to push back the German defensive line towards Haig's original target, Bapaume. However, during the last phase of the Somme offensive in October and November, the Germans held their ground against a series of unsuccessful attacks. As mud and rain began to make conditions impossible, the Battle of the Somme was finally brought to a halt on 18 November.

In his draft plan of the Somme attack, Rawlinson envisaged a bold advance in which the Allies killed 'as many Germans as possible with the least loss to ourselves'. When the campaign was ended, the first-day objective of Bapaume still lay six miles distant.

While German casualty rates were indeed high - roughly 450,000 men killed or wounded - Britain and France fared even worse, with a combined total of 650,000 casualties. The unprecedented carnage of the Battle of the Somme marked a turning point in public perceptions of the war in Britain. In military terms, it was the first time that the Allied strategy of pursuing a 'war of attrition' was seriously brought into question. Nonetheless, it was not until 1918 that the Allies adopted a more flexible and mobile method of attack on the Western Front.

In the meantime, as the British prime minister David Lloyd George remarked after the Battle of Passchendaele (July-November 1917), it was hard to avoid the impression that 'Haig does not care how many men he loses. He just squanders the lives of these boys.'