Title of Movie?

Maybe this post does not go in this forum, but...

Forgot the title of a movie I saw a long time ago. It basically was that a medic was on a wagon train escorted by Infantry and Cavalry. Native Americans were on the warpath. A doctor is with the column. Native Americans were infected with Smallpox after an outbreak in the column, a discarded bandage or handkerchief. The column commander was infected as well, and the doctor is forced to take command. At some point the doctor orders the Infantry and civilians ahead but keeps the wagons circled, and the cavalrymen disguised as civilians. When some Native Americans attack, the wagon train moves ahead. There is a cannon in the last wagon. So the wagons continue to a pass, where the Infantry has taken positions.