I nominate "Ulzana's Raid." It has the inevitable young lieutenant just out from West point who the equally inevitable Old Scout (Burt Lancaster) has to take in hand during an Apache rampage. They leave the fort in pursuit of the vicious Ulzana and the first lesson the Lt. has to learn is that, in Apache country, it's all about horses. Too often in movies horses are treated like machines that never get tired or hungry or thirsty. Not in this one. After finding a massacred settler family the lieutenant wants to know if they can catch up with the Apaches before they reach the next ranch. The scout tells him they could, but by the time they arrived, their horses will be worn out and the Apaches will be on fresh remounts from the ranch. So they have to let that ranch get the Apache treatment while they let their horses rest and recuperate, in hopes of catching the Apaches before they get to another ranch down the valley. Likewise, the scout explains, Ulzana has horse problems, too. Can he keep finding fresh horses for his men? Apaches tend to ride horses to death and then steal new ones. If he can't, his men will leave and go home because they are not any sort of disciplined army and will only follow a man as long as he leads them to excitement and loot. This was one of the best, most realistic Indian-fighting and "horsiest" of the Hollywood films.