(July 1–Nov. 13, 1916), costly and largely unsuccessful Allied offensive on the Western Front during World War I.

The Germans were securely entrenched and strategically located when the British and French launched their frontal attack on a 21-mile (34-kilometre) front north of the Somme River. A week-long artillery bombardment preceded the British infantry's “going over the top,” but the latter were nevertheless mown down as they assaulted the virtually impregnable German positions. The British sustained nearly 60,000 casualties (20,000 dead) on the first day of the attack. The Somme offensive then deteriorated into a battle of attrition. In September the British introduced their new weapon, the tank, into the war for the first time, but with little effect. In October torrential rains turned the battlefield into an impassable sea of mud, and by mid-November the Allies had advanced only 5 miles (8 km).

Although the figures have been much disputed, the casualties from the First Battle of the Somme perhaps amounted to roughly 650,000 German, 195,000 French, and 420,000 British. The Battle of the Somme became a metaphor for futile and indiscriminate slaughter. By taking the offensive in the Somme, the Allies did manage to relieve the German pressure on Verdun (Verdun, Battle of), however, and the subsequent fighting did much to wear down the German army by destroying its prewar cadres.