First World War: The British Royal Navy launched unsuccessful raids on Ostend and Zeebrugge in German-occupied Belgium.

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 Royal Navy (RN) is the naval warfare force of the United Kingdom. It is a component of His Majesty's Naval Service, and its officers hold their commissions from the King. Although warships were used by English and Scottish kings from the early medieval period, the first major maritime engagements were fought in the Hundred Years' War against France. The modern Royal Navy traces its origins to the English Navy of the early 16th century; the oldest of the UK's armed services, it is consequently known as the Senior Service.

The First Ostend Raid was the first of two attacks by the Royal Navy on the German-held port of Ostend during the late spring of 1918 during the First World War. Ostend was attacked in conjunction with the neighbouring harbour of Zeebrugge on 23 April in order to block the vital strategic port of Bruges, situated 6 mi inland and ideally sited to conduct raiding operations on the British coastline and shipping lanes. Bruges and its satellite ports were a vital part of the German plans in their war on Allied commerce (Handelskrieg) because Bruges was close to the troopship lanes across the English Channel and allowed much quicker access to the Western Approaches for the U-boat fleet than their bases in Germany.