World War II: The submarine HMS Oxley is mistakenly sunk by the submarine HMS Triton near Norway and becomes the Royal Navy's first loss of a submarine in the war.

World War II or the Second World War was a global conflict between two coalitions: the Allies and the Axis powers. Nearly all of the world's countries participated, with many nations mobilising all resources in pursuit of total war. Tanks and aircraft played major roles, enabling the strategic bombing of cities and delivery of the first and only nuclear weapons ever used in war. World War II is the deadliest conflict in history, causing the death of 70 to 85 million people, more than half of whom were civilians. Millions died in genocides, including the Holocaust, and by massacres, starvation, and disease. After the Allied victory, Germany, Austria, Japan, and Korea were occupied, and German and Japanese leaders were tried for war crimes.

HMS Oxley was an Odin-class submarine of the Royal Australian Navy (RAN) then Royal Navy (RN). Very slightly off course, near Obrestad, on the south-western cape of Norway, she was hit by friendly fire seven days after the start of World War II costing 53 lives and leaving two survivors.

HMS Triton was a submarine of the Royal Navy named for the son of Poseidon and Amphitrite, the personification of the roaring waters. She was the lead ship of the T class of diesel-electric submarines. Her keel was laid down on 28 August 1936 by Vickers Armstrong at Barrow-in-Furness. She was launched on 5 October 1937, and commissioned on 9 November 1938.

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.