In 1917, which war does the British mission take place during?

The British mission in 1917 takes place during World War I.

Sam Mendes directed and co-wrote the film, which follows two British soldiers ordered to carry a message across German-held territory. Their task is to stop an impending attack that could trap thousands of British troops, including the brother of one messenger.

The story is set in northern France in 1917, during the trench warfare of the Western Front. Although the characters and mission are fictional, Mendes drew inspiration from stories told by his paternal grandfather, Alfred Mendes, who served as a messenger during the war.

The film is famous for appearing to unfold in one continuous shot. In reality, its long takes are joined through carefully planned cuts, camera movements and changes in lighting or scenery. The technique serves the immediacy of the mission rather than changing its historical setting.