The first & more watchable of 2 intense Westerns from Ralph Nelson, "Diablo" is one of the starkest examples of the tough, realistic Westerns that became popular in the late 1950s. Professional scout Remsberg (Garner) is out for vengeance on the "civilized" men who butchered his Comanche wife. His quest is interrupted when he's tasked to accompany an Army ammo convoy led by ambitious Lt. McAllister (Travers). Along for the ride are wrangler & ex-sergeant Toller (Poitier), shopkeeper's wife Ellen (Andersson), a former captive of the Apache who's regarded with disgust by her white neighbors, and her embittered husband (Weaver). They're intercepted by a large war party of the same Apaches who once held Ellen captive. As with films of this kind from "The Last Wagon" to "Ulzana's Raid," the male lead is a white man who understands the plight of the Indians, sympathizes with them but nevertheless works for the whites. There's nary a letup in the darkness & intensity. Ellen, the tortured, exploited victim of both sides, is no love interest, while the only humor in the film comes in occasional rueful exchanges among the tough guys. But there's plenty of action in scenes as well-done as any of the period & budget. What makes "Diablo" stand out is the clever, seamless depiction of the strategy as the ambushed convoy spars with the wily, ruthless Apache. It's far more engrossing than almost any war movie, including those with budgets many times larger. Andersson doesn't have much to work with but Garner & Poitier play their tough guys with just the right balance between expression & terseness. Weaver makes the most of his limited opportunity to develop the selfish husband who feels sorrier for himself than his wife over her horrifying torment. "Diablo" delivers action & adventure that never lags, along with a strong dose of historical-social awareness, but it's not the ticket for a light evening's entertainment. Director Nelson plays the colonel commanding the relief force.