Battle of the Somme
Military action
Mostly British offensive. Another disaster of 1916 in the West.
While the battle of Verdun raged, British Empire decided to test its new army - that wasn't composed of regular soldiers from before the war started. They had manpower and firepower greater than the enemy. Why not use that? Especially as they could also force German Empire to redirect its forces from Verdun offensive.
The battle, however, ended in a bloody - and ultimately inconclusive - massacre, even despite Entente using tanks for the first time.