World War I: Tanks are used for the first time in battle, at the Battle of the Somme.

World War I or the First World War, also known as the Great War, was a global conflict between two coalitions: the Allies and the Central Powers. Main areas of conflict included Europe and the Middle East, as well as parts of Africa and the Asia-Pacific. There were important developments in weaponry including tanks, aircraft, artillery, machine guns, and chemical weapons. One of the deadliest conflicts in history, it resulted in an estimated 30 million military casualties, plus another 8 million civilian deaths from war-related causes and genocide. The movement of large numbers of people was a major factor in the deadly Spanish flu pandemic.

The development of tanks in World War I was a response to the stalemate that developed on the Western Front. Although vehicles that incorporated the basic principles of the tank had been projected in the decade or so before the War, it was the alarmingly heavy casualties of the start of its trench warfare that stimulated development. Research took place in both Great Britain and France, with Germany only belatedly following the Allies' lead.

The Battle of the Somme, also known as the Somme offensive, was a battle of the First World War fought by the armies of the British Empire and the French Republic against the German Empire. It took place between 1 July and 18 November 1916 on both sides of the upper reaches of the river Somme in France. The battle was intended to hasten a victory for the Allies. More than three million men fought in the battle, of whom more than one million were either wounded or killed, making it one of the deadliest battles in human history.