The Long-Knives 4: Gunsmoke at Powder River - The Long-Knives, #4

U.S. Army Captain Charles Riker had been ordered to march his company of social misfits and raw recruits deep into Sioux territory. It was a land of heat and blistering winds where daydreaming could separate a man from his scalplock, and when Indian patrols spot the bluecoated interlopers they set upon the troopers with burning powder and hot lead.
Riker and his struggling command turn back—only to find their retreat to the main body of troops has been cut off by the avenging Sioux.
Outnumbered hundreds-to-one in a Montana wilderness where good men could be living one moment and dying the next, Riker must lead his band across long miles of open country to the nearest army post at Tongue River. But between them and the fort ride fierce warriors aiming to add bluecoat scalps to the ones already hanging on the tribal lodge poles. Short on rations and ammunition, but long on determination and guts, Riker's column begins its hell trek to freedom while hundreds of Plains Indians close in for the kill.