British warships win the first naval battle of the war at Heligoland Bight, sinking three German cruisers. Britain has the most powerful navy in the world: 29 modern battleships to Germany's 19. They now impose a naval blockade on Germany, preventing contraband goods, including food, from reaching it by sea. The aim is to bring Germany's economy to its knees and force it to surrender. But a week later, the British cruiser HMS Pathfinder becomes the first victim in history of a lethal new weapon - the submarine-launched torpedo.
German submarines, or U-boats, have a surface range of 9000 miles, and can attack undetected from beneath the waves. They herald a deadly new challenge to Britain's command of the seas.