In 1781, he joined the army and was put in service under the Marquis de Lafayette, who was desperately trying to fight the chaos caused in Virginia by turncoat soldier Benedict Arnold. His forces diminished by British Gen. Charles Cornwallis' troops, Lafayette needed reliable information about enemy movements.
Armistead began his work posing as an escaped slave, entering Arnold's camp as an orderly and guide, then sent what he learned back to Lafayette. He later returned north with Arnold and was posted close enough to Cornwallis' camp to learn further details of British operations without being detected. By also being used as a British spy (who fed them inaccurate data), Armistead was able to travel freely between both sides. One day, he discovered that the British naval fleet was moving 10,000 troops to Yorktown, Va., making it a central post for their operation.
Using the intricate details Armistead provided, Lafayette and a stunned, but relieved George