From American Heritage Magazine Feb 1973:
During the War of 1812, there were over five thousand American POWs in HM Dartmoor Prison in England. They were sailor privateers, merchant seamen and men impressed into British service. Occasionally there were people other than sailors. They were from New York, Salem, Baltimore, New Orleans, and other American ports. During that war, there were over 20,000 American seamen in Dartmoor, the Cape of Good Hope, and Nova Scotia. If you had some ancestors disappear perhaps that’s why. There is more on Dartmoor at www.dartmoor-prison.co.uk. The magazine article is there also and it will be in the ACGS collections. You can find lists of War of 1812 prisoners online.