made goods carried on neutral ships lawful prizes of war. The British responded in 1807 with Orders in Council which similarly forbade any shipping to France. By 1807, when Napoleon introduced his Milan Decree, declaring all ships touching at British ports to be legitimate prizes of war, it had become almost impossible for the U.S. to remain neutral. Between 1804 and 1807, 731 American ships were seized by Britain or France for violation of one of the blockades, roughly two thirds by Britain. Since the Jay Treaty, France had also adopted an aggressive attitude to American neutrality. Whereas Britain, through a process known as pre-emption, compensated American ship owners for their losses, France did not. French frigates burned American grain ships heading for Britain and treated American sailors as prisoners of war. U.S.–French relations had soured so much that by 1812, Madison was also considering war with France. As a result of these increasing trade volumes during the Napoleonic Wars the United States Merchant Marine became the world's largest neutral shipping fleet. Between 1802 and 1810, it nearly doubled, which meant that there were insufficient numbers of experienced sailors in the United States to man it. To overcome this shortfall, British seamen were recruited, who were attracted by the better pay and conditions. It was estimated that 30% (23,000) of the 70,000 men employed on American ships were British. During the Napoleonic Wars, the British Royal Navy expanded to 600 ships, requiring 140,000 sailors. The Royal Navy could man its ships with volunteers in peacetime, but in wartime, competing with merchant shipping and privateers for the pool of experienced sailors, it turned to impressment from ashore and at sea. Since 1795 the Quota System had been in use to feed men to the navy but it was not alone sufficient. Though most saw it as necessary, the practice of impressment was detested by most Britons. It was illegal under British law to impress foreign sailors, but it was the accepted practice of the era for nations to retrieve seamen of their own nationality from foreign navies during times of war. However, in the nineteen years Britain was at war with France prior to the war of 1812 some ten thousand American citizens were impressed into the British navy. The American ambassador in London, James Monroe, under President Thomas Jefferson, protested to the British Foreign Office that more than fifteen thousand