In 1855 Appleton was sent as diplomatic envoy to London, England to promote United States interests in negotiations to end the Crimean War. He returned to the United States in 1857 and was appointed as the fourth Assistant Secretary of State, a post he held for the following three years.
In 1855, Appleton was assigned as a diplomatic envoy to London, England to represent United States interests during negotiations regarding the Crimean War. He returned to the United States in 1857 and was appointed as the fourth Assistant Secretary of State, a position he held for three years.