In New Mexico after the Civil War, Capt. Richard Lance (Gregory Peck) leads a detachment of soldiers, including scout Joe Harmony (Jeff Corey), to Ft. Invincible. Hostile Apache Indians have burned the fort to the ground and killed its soldiers. Lance captures Tucsos (Michael Ansara), the chief, and takes his prisoner to Ft. Winston.
Commanding officer Col. Drumm (Herbert Heyes) says the undermanned fort won't be able to fight off an Apache rescue effort, and orders Lance to choose an officer to head a detail to take Tucsos to the better defended Ft. Grant. Knowing the detail may not get through, Lance decides to lead it himself. He then visits his love, Cathy Eversham (Barbara Payton), a captain's daughter. But, Cathy's other admirer, Lt. William Holloway (Gig Young), is already there. After Lance tells Cathy goodbye, Holloway proposes, but she refuses him because she is in love with Lance. Holloway affectionately kisses Cathy, and Lance, who is passing by, sees the kiss.
Drumm is very ill. He learns that Lance intends to lead the detail, and orders him to send Holloway instead because Lance is the only officer he trusts to run the fort if he becomes too sick. After Lance delivers the new orders to Holloway, Cathy is convinced that he changed the orders to eliminate his rival. Several days later, the detail returns with Holloway's body. When Harmony reports that Holloway was tortured by the Apaches before he died, the entire fort turns against Lance, and Trooper Kebussyan (Lon Chaney Jr.), one of the survivors, tries to kill him.
Harmony believes that Tucsos, knowing the fort is vulnerable, will attack before reinforcements can arrive. To buy time, Lance convinces Drumm to allow him to lead a patrol to Ft. Invincible and try to hold the pass until an expected relief column of 400 soldiers arrives.
For the patrol, Lance purposely picks misfits and those who hate him the most: Lt. Jerry Winters (Dan Riss), who is dying of tuberculosis; Corp. Timothy Gilchrist (Ward Bond), a drunk; Sgt. Ben Murdock (Neville Brand), who hates Lance for blocking his promotion; Trooper Onstot (Steve Brodie), a deserter from the Confederate Army; Kebussyan; Harmony; Trooper Rutledge (Warner Anderson), who is motivated by revenge; and Trooper Saxton (Terry Kilburn), a coward.
Over the next few days, several attempts are made on Lance's life. Tucsos learns that there are only thirty-one men in the relief column, not the 400 who were expected. Onstot and Murdock are captured, and Tucsos' Indian braves attack the fort. After the Apaches retreat, Lance sends Winters to intercept the relief column and redirect them to Ft. Invincible. As he leaves, Winters is wounded, but is able to continue.
At night, during another assault, Rutledge is killed, and Kebussyan is wounded. The next morning, the Apaches discover Lance and Kebussyan in the pass, and attack. Before he dies, Kebussyan holds off the Indians until Lance sets off the dynamite, blocking the pass almost completely. Only Lance, Gilchrist and Saxton are left alive, and they have no water.
Once again, the Indians storm the fort. The situation appears to be hopeless, but just then the relief column of thirty-one soldiers arrives. The Indians turn their attack toward the new soldiers, who fire on them with a Gatling gun, which fires 350 rounds per minute. Faced with this new weapon, the Indians surrender. Tucsos manages to reach the fort, and after a struggle, Lance kills him with his own knife. When he returns to Ft. Winston, Lance learns he has been made acting commander, as Drumm has left his post because of ill health. Later, Lance is reunited with Cathy, who now knows that he was not responsible for Holloway's death.
A 1951 American black & white B-Western film (a/k/a "Fort Invincible") directed by Gordon Douglas, produced by William Cagney (younger brother of James Cagney), screenplay by Edmund H. North and Harry Brown, based on the 1943 novel of the same name by Charles Marquis Warren, cinematography by Lionel Lindon, starring Gregory Peck, Barbara Payton, Ward Bond, Michael Ansara, Gig Young, Lon Chaney Jr., and Neville Brand.
Lon Chaney Jr. and Barbara Payton would be reunited the same year in "Bride of the Gorilla" (1951).
Gregory Peck considered this role to be a low point of his career. He regarded it as a potboiler and a step backward for his career coming off the success, starring in "The Gunfighter" (1950). During filming he had an affair with Barbara Payton.
Trooper Onstott is referred to as a "Reb from a prison camp" (also known as "galvanized Yankee"). This refers to captured Confederate soldiers in POW camps who took an oath of loyalty to the Union, mainly to get out of the camps, but were not to be sent against their former comrades. Instead, they were sent west to fight Indians.
A tension building oater with a noir vibe and a "Dirty Dozen"-aspect shot cheaply on a studio set, and Peck. He could ‘lift’ a mediocre picture, and that’s what he did here.