In wartime, Britain depended on civilian cargo ships to import food and raw materials, as well as to transport soldiers overseas, and keep them supplied. The title 'Merchant Navy' was granted by King George V after the First World War to recognise the contribution made by merchant sailors.
Britain’s merchant fleet was the largest in the world during both world wars. In 1939, a third of the world’s merchant ships were British, and there were some 200,000 sailors. Many merchant seamen came from parts of the British Empire, such as India, Hong Kong and west African countries. Women also sometimes served at sea in the Merchant Navy.
During both world wars, Germany operated a policy of 'unrestricted submarine warfare', or sinking merchant vessels on sight. By the end of the First World War, more than 3,000 British flagged merchant and fishing vessels had been sunk and nearly 15,000 merchant seamen had died. During the Second World War, 4,700 British-flagged ships were sunk and more than 29,000 merchant seamen died.
Since the Second World War, the British Merchant Navy has become steadily smaller, but has continued to help in wartime, notably during the Falklands War.
This article was edited by Jeremy Ottevanger. Several IWM staff contributed to an older version of this piece.