What 1916 battle on the Western Front saw over a million casualties?

The 1916 battle on the Western Front that saw over a million casualties was the Battle of the Somme.

Fought from 1 July to 18 November 1916, the Somme offensive was launched by British and French forces against Germany in northern France. The Allies hoped to relieve pressure on the French army at Verdun and break through German defenses. More than three million troops took part, and combined killed, wounded, missing, and captured exceeded one million.

The battle is especially remembered for its catastrophic opening day, when British forces suffered 57,470 casualties, including 19,240 dead—the worst single-day loss in British military history. Tanks were also used operationally for the first time during the Somme campaign, in September 1916.

Casualty totals vary because wartime armies counted losses differently, but the scale is undisputed. Verdun was also extraordinarily bloody, yet the question’s million-plus figure most conventionally identifies the Somme.