Dyeing for Your Art: Natural blonde Darren Nesbitt's hair is such an unusual shade because it had to be dyed twice. He was supposed to get it dyed back to blonde from another color (he often appeared with brown or black hair in films). But an accident with the process turned his hair green, forcing them to dye it again, turning it that unnatural-looking shade of platinum blonde.
So My Kids Can Watch: Specifically written by Alistair MacLean to give his mate Richard Burton a good old-fashioned adventure romp to show the kids (said kids wanted to see their dad in something that wasn't highbrow).
What Could Have Been: Lee Marvin was offered the role of Schaffer, but he declined, telling the producers they were about 4 years too late. Marvin had already starred in a WW2 action-adventure, The Dirty Dozen, which he hated. Although it made him a huge star, he did not want to return to that type of movie.
Michael Caine later claimed to have turned down the role of Major Smith.