The Northern Patrol was an operation of the British or Royal Navy during the First World War and again during the Second World War. The Patrol existed to form part of the British "distant" blockade of Germany. Its main task was to prevent trade to and from Germany by checking merchant ships and their cargoes. In addition it was to stop German warships, raiders and other German naval ships to leave the North Sea into the Atlantic Ocean or enter the North Sea from the Atlantic, protect the Shetlands against invasion and gather intelligence from intercepted neutral ships.