James Coburn's friend Robert Vaughn recommended him to director John Sturges for the last remaining lead, the role of Britt. Sturges said he needed a Gary Cooper type of actor, and Vaughn said Coburn was the actor he needed.
James Coburn (Britt) and Robert Vaughn (Lee) have only 11 and 16 lines in the entire film respectively. Although they were close friends for almost 50 years, this is their only film together.
In the television series [The Man From U.N.C.L.E.], American agent Napoleon Solo is played by American actor Robert Vaughn, and Russian agent Illya Kuryakin is played by UK actor David McCallum (from Scotland). In the movie, it is the reverse: Solo is played by UK actor Henry Cavill (from England) and Kuryakin is played by American actor Armie Hammer.