World War II: British Royal Navy and Royal Australian Navy forces defeat those of the Italian Regia Marina off the Peloponnesian coast of Greece in the Battle of Cape Matapan.

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.

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 Royal Australian Navy (RAN) is the naval branch of the Australian Defence Force (ADF). The professional head of the RAN is Chief of Navy (CN) Vice Admiral Mark Hammond. The Chief of Navy is also jointly responsible to the Minister for Defence (MINDEF) and the Chief of the Defence Force (CDF). The Department of Defence, which is a part of the Australian Public Service, supports the ADF, and ergo, the Royal Australian Navy.

The Regia Marina (RM) or Royal Italian Navy was the navy of the Kingdom of Italy from 1861 to 1946. In 1946, with the birth of the Italian Republic, the Regia Marina changed its name to Marina Militare.