pyenme;
In the Film "Fort Apache" One hour 51 Minutes in to the Film after Fonda sends Duke to the Rear with the Wagons, He rides by His Troops and said "Good Luck B - Troop" and Rides to the Rear. 
In the Film "She Wore a Yellow Ribbon" One Hour and 19 Minutes in to the Film, after He is given the Silver Watch and He rides away, He said "Good Luck C - Troop." 
Chilibill 
The film that Duke got the Pocket Watch from His Troops before leaves the Army Horse Solders at the Fort is "She Wore A Yellow Ribbon" done in Monument Valley in the Late 1940s. 
How do I know? I was one of the Horse Solders in front of Him as he is given the watch.
For a little picture story of the film go to the Site Below and at almost the end of the Picture you will see of Duke Getting the Watch. Because of all pictures it might take time to load.
Chilibill
