In mid-April 1941, during World War II, German Field Marshal Erwin Rommel(James Mason) and his Afrika Korps have driven the British Army into headlong retreat across North Africa toward Egypt and the vital Suez Canal. Standing in Rommel's way is Tobruk, a constant threat to his supply lines. The9th Australian Division are asked to hold the port for two months, at which time they are to be relieved.
The defending Allied general (Robert Douglas) chooses English Captain "Tammy" MacRoberts (Richard Burton), an experienced field officer, to take command of a company of newly arrived, green Australian troops. The no-nonsense MacRoberts is disliked by the undisciplined Australians. He is surprised to see in their ranks his former schoolmaster, Tom Bartlett (Robert Newton). Bartlett, an alcoholic, later explains that after being dismissed from his job in Britain due to his drinking, he went to Australia and joined the army while intoxicated. MacRoberts offers to transfer him to a safer billet, but Bartlett turns him down.
Because of the desperate situation, the inexperienced troops are sent directly into the front line. The men dig foxholes and prepare for Rommel's certain attack. The Allied general masses his artillery where he guesses the Germans will strike. His gamble pays off. Under cover of a sandstorm, they attack exactly where the general predicted and head directly at MacRoberts' men. In the fierce battle, Captain Currie is wounded. Lieutenant Harry Carstairs (Charles Tingwell) abandons his vital post to go to his aid, in vain. After the Germans are beaten back, an infuriated MacRoberts vows to have Carstairs court-martialed for disobeying orders and leaving a dangerous hole in the line, but Bartlett persuades MacRoberts to retract his request.
MacRoberts receives a field promotion to major, then a temporary one to lieutenant colonel after the general elevates him to command of his battalion of Australians. The general then decides to erode the besiegers' confidence by sending out smallcommando raids every night. MacRoberts' patrols do their part in exacting a toll on the enemy.
One day, the general worries about reports of German heavy artillery being moved up, indicating an attack is imminent. The suspected location of the artillery's ammunition dump is too far away to be attacked by the usual nighttime raid, so MacRoberts proposes using trucks abandoned by the Italians to drive there in disguise and blow it up. MacRoberts leads 54 picked men in three trucks. The attack is a success, but Carstairs is killed and MacRoberts is wounded and captured. While he is being attended to, he meets Rommel, who has been shot by a strafing Spitfire. Although he is respectful to the field marshal, MacRoberts defiantly points out that Tobruk is a thorn in his side. Rommel is bemused by his brashness and orders that he be treated well.
Later, as the prisoners are being transported, their trucks are attacked by RAF fighter aircraft. In the confusion, MacRoberts and Sergeant "Blue" Smith (Chips Rafferty) get away. After an exhausting walk through the desert, they reach friendly lines. The Australians have now held on for eight months.
In November, the general tells his officers that a relief column led by General Claude Auchinleck is headed for Tobruk. However, they need to take control of a key hill that overlooks the road that Auchinleck must use. The general asks MacRoberts to take his best company and hold the position for three days. On the morning of the ninth day, fearing that the men can take no more, MacRoberts orders a retreat, though Bartlett begs him to ask the men to hang on. To MacRoberts' surprise, the men refuse to leave. Bartlett overcomes his self-professed cowardice by manning the forward observation post, where survival is measured in hours. Just after the Germans bombard the hill, the Australians hear bagpipes announcing the arrival of Auchinleck's troops. After a hard-fought 242 days, the Allies have relieved Tobruk.
- Richard Burton as Captain "Tammy" MacRoberts
- James Mason as Field Marshal Erwin Rommel
- Robert Newton as Tom Bartlett
- Robert Douglas as the General
- Torin Thatcher as Colonel Barney White
- Chips Rafferty as Sergeant "Blue" Smith
- Charles "Bud" Tingwell as Lieutenant Harry Carstairs (as Charles Tingwell)
- Charles Davis as Pete
- Ben Wright as Mick
The film is based on the Australian 9th Division, who were charged with the defence of Tobruk under the command of General Leslie Morshead. Hoping to survive against overwhelming odds for two months, the garrison held off the best of Rommel's Afrika Korps for over eight months. Morshead was a distinguished Australian citizen-soldier, but is depicted in the film as the anonymous "General" and played by English actor Robert Douglas.
The film was a quasi-sequel to The Desert Fox: The Story of Rommel (1951), partly made to portray a less likeable General Rommel, after criticism that film had been too friendly to the Germans. Rommel is again played by James Mason only this time he usually speaks in German and is not sympathetic. The title "Desert Rats" was selected to refer to the earlier title "Desert Fox". Mason wore Rommel's real scarf in the film, which had been given to him by the general's widow.
Michael Rennie was originally announced to play to male lead opposite Robert Newton, but eventually the role was taken by Richard Burton. Instead, as he had done in The Desert Fox several years earlier, Rennie delivered an uncredited voiceover.
The script was written by an American, Richard Murphy, who was familiar with Australian servicemen from his time being a liaison officer with the Ninth Division in New Guinea, after its withdrawal from the Middle East in 1942. Several genuine Australian actors were cast, including Chips Rafferty, Charles Tingwell, Michael Pate and John O'Malley. Tingwell and Rafferty were flown to Hollywood from Australia.
Australian journalist Alan Moorehead was used as a consultant and the technical adviser was an Englishman now in theCanadian Army, Lieutenant George Aclund, who took part in the defence of Tobruk.
The battle sequences were shot near Borrego Springs, a Californian desert town. Some background scenes were taken from the documentary Desert Victory (1943).