WW-II movie map of Africa valet spy

This is for you old timers! I'm trying to find this B&W film about an (English?) spy in the German army camp in Africa (I think Northern part). I remember he is a valet to a General (?) and finds a map and the secret to the map is five letters spaced across the face of the map. I thought the spy was played by James Mason but cannot find anything in his biography. I also thought the five letters were prominent in the title; something like "five .... to cairo" but I get nowhere with any combinations I can think of. It was a very good movie and, if I can track down the title, I would like to find a copy.
I tried to peruse WWII films but there were so many!
Any help?

Five Graves to Cairo, directed by Billy Wilder. Franchot Tone plays the spy and Erich von Stroheim is the general.

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Yeah, I just found it, too. I was mistaken about James Mason; it was Franchot Tone.
Argg. And expensive, too!!
Thanks

I saw that movie on either TCM or AMC within the last 4 years, so it might be available other than by buying.

Good luck finding it.