The rebel plan

Siege at Red River happens about November 9, 1864, the date of a newspaper read at the beginning, to April, 1865, when the characters hear that the Rebels have abandoned Petersburg and Richmond but do not hear of Lee's surrender.

The Rebel spies capture a Gatling gun, one of just a very few prototypes, in Ohio, and try to take it to Rebel territory to use it in battle and/or make copies of it. They take it southwest and wind up somewhere in Kansas, I think.

The fictional town is somewhere near Lawrence, and near a fictional Fort Smith, which has a federal garrison and so is not the famous Fort Smith, Arkansas, which was probably Rebel controlled at that time. The plan is to take the Gatling gun across Indian territory to Rebel Territory, and thus probably to cross The Indian Territory (which is now Oklahoma) into Texas.

Thus the Red River in the title should be the Red River of the South between Oklahoma and Texas and not the Red River of the North or any fictional Red River of the Middle.

The Rebel spies with the Gatling gun travel so slowly that it takes them 5 months to reach the border of Rebel territory and then lose the Gatling gun just when the South is being finally defeated and basically can't put the super weapon to use any longer.

I guess a better plan would be to travel north from Ohio to neutral Canada where Rebel agents might build a factory and manufacture Gatling guns and ammunition. Of course the Union would be building bigger factories turning out Gatling guns and ammunition faster. Then there would be the little problem of getting the Rebel Gatling guns and ammunition out of Canada and into the hands of the Rebel army.

The best way to do that would probably be to ship them from Canada and try to run the blockade into Wilmington, North Carolina, the last unoccupied Rebel port, and send them to the Rebel armies.

I think that would have been a much better Rebel plan and might actually have had a slight degree of success. Of course if the scriptwriters used that plan the movie wouldn't be a western.