Tales my father told me when I was young.  
On one particular occasion, when I was on watch in the port of Liverpool during the First World War, I was instructed to expect a special consignment to be brought on board during the evening. Late at night, an army lorry arrived with an armed escort, and the soldiers brought on board several heavy boxes and stowed them in the safe in the Purser's Cabin. I was entrusted with the key.
Having been sworn to secrecy beforehand, we sailed the following morning to New York, where the boxes were taken away just as mysteriously by the Military. Only the Captain and I knew what was inside those boxes.
They contained
gold bullion from the British Government. It was in part payment for the supply of munitions from the United States for the war effort.
That key burned a hole in my uniform pocket all the way across the Atlantic until it was safely handed over to the authorities in New York.