Location shooting in Hong Kong was refused by the country's government on the grounds of possible breach of the peace following demonstrations and propaganda campaigns mounted by Hong Kong communists claiming the film was anti Mao and anti Chinese consequently filming was transferred to Taiwan (Kine Weekly 7/12/68)
Originally intended as a starring vehicle for Frank Sinatra with Yul Brynner and Spencer Tracy co-starring.
Peck later described the implanted transmitter device "a bit hard to swallow".
Effigies of Gregory Peck were burned in China due to the perceived view that this film was anti-Maoist.