Who is Cartwright Jones in the novel, Where Eagles Dare?

Cartwright Jones is an American actor who is hired to play American General Carnaby. M.I.6 arranges for Jones to be captured by the Germans and taken to Schloss Adler just before the novel starts, and at first every member of the team except for Smith believes that their mission is to rescue the general. Jones is indeed rescued by Smith and Schaffer and accompanies them, as well as Mary and Heidi, back to England on the rescue plane.