in 1866, thomas was asked to join the french naval force as an interpreter to go to korea as a part of invading party. however, the french force went to vietnam instead. so thomas took a job as an interpreter on an armed american trading ship, the "general sherman". thomas persuaded the captain to sail to pyongyang to establish trade between the united states and korea, even though uninvited trade was forbidden. thomas's personal motivation was to spread the gospel in korea.