Old Oklahoma Plains

In 1926, the U.S. Cavalry is planning maneuvers to test the efficiency of tanks against horsemen. Rex Allen, an ex-Cavalry man turned rodeo performer, has been asked by Col. Charles Bigelow to herd the cattle from nearby ranches off a free-range pasture owned by the government to clear it for testing. The uncooperative ranchers, who fear the permanent loss of free grazing land, are being agitated by Chuck Ramsey, an embittered Army veteran who was court-martialed for gambling and insubordination. Secretly manipulating Chuck is Arthur Jensen, whose family fortune was made selling horses to the Army. Rex and his men report to Bigelow, where Rex meets Lt. Spike Conners, the mechanic who is assisting Bigelow, and Spike's sweetheart, Terry Ramsey, who is concerned about her brother Chuck's gambling fever. Terry invites Rex to a meeting of the ranchers hosted by Chuck at the Ramsey ranch, but Chuck inflames the ranchers so that when Spike, Rex and his assistant, Slim Pickens, arrive, the ranchers beat them up. Terry tries to shame Chuck for his part in the brutality, but he accuses her of selling out the ranchers because of her romance with Spike. Though injured, Rex and his assistants begin herding the stock off the government pasture, while Jensen and Chuck make plans to sabotage the tests. On the day of the maneuvers, Chuck and Nat Cameron, an employee of Jensen, boobytrap the area with explosives. As important Army officials watch, the maneuvers, which are designed as a race between a tank driven by Spike and a troop of Cavalrymen, crossing flat areas, rock barriers and water, begin. When confronted with a barbed wire fence, the horsemen dismount to pull it down, but the tank barrels through it and takes the lead. Rex, who is watching the race from a distance through binoculars, spots some men moving the flag markers and changing the race course. Sensing trouble, he and Slim ride out to warn Spike, but the tank explodes. Bigelow, who is Spike's passenger, is injured, while Spike dies instantly. At Spike's military funeral, Terry tells Rex that she is selling her part of the ranch to Chuck, but Rex asks her to delay because he suspects Spike's death was not an accident. Bigelow's supervisors, believing the explosion was due to mechanical failure, order him to close the testing site and chastise him for wasting time, money and personnel. Rex, who is unable to find the men who moved the flags, shows Bigelow a casing for dynamite found in the wreckage, and says that he believes it is the kind of explosive ranchers use for blowing up tree stumps. Bigelow, risking court-martial, gives Rex permission to move the repaired tank to the Ramsey ranch and try to find Spike's killer. Outside a nearby casino, Chuck reports to Jensen that the Army is moving out and asks for his payoff. Slim shows up, and feigning drunkenness, tells the ranchers there that new tests are being planned for the tank, which is now in the Ramsey barn. When Rex and his men overhear Jensen urging the ranchers to "take care of Rex and Bigelow," Rex sends Slim to hide the tank and tells the disbelieving ranchers that the tank was sabotaged. When the ranchers are unmoved by his plea for patriotism and try again to gang up on Rex, Rex's men hold them back, so that Rex beats Cameron in a fair fight. By then, Chuck and Jensen have slipped away and, with Jensen's henchmen, storm the Ramsey barn. Though Terry tries to intervene, a gunfight erupts between Slim and the ranchers, and Jensen orders Chuck to enter through the back. Rex and his men ride up and the shootout continues. Chuck, who is realizing it has gone too far, wants to give up. At gunpoint, he is forced into the tank with Jensen and told to drive it out of the barn. Rex chases on horseback, but the tank tumbles sideways down a hill, and Jensen is killed. With his dying breath, Chuck expresses regret for his traitorous activities, after which Rex's men apprehend Jensen's henchmen. The tank is repaired, and Bigelow, who is given permission to continue the testing, finds alternate grazing land for the ranchers. Having completed their task, Rex rides away, followed by Slim.