It tells the story of the siege of Tobruk, April-November 1941. The German advance from Libya into Egypt has cut off the vital Libyan port of Tobruk, which remains in Allied hands. Captain "Tammy" MacRoberts (Burton) is given command of a company of green troops from Australia who lack a senior officer. The free-spirited, boisterous Australian soldiers don't much care for their new no-nonsense CO, and he is rather unimpressed by his undisciplined raw recruits. MacRoberts does however find one friendly face, and it's quite a surprise: his old schoolmaster Tom Bartlett, who lost his teaching position due to alcoholism and made his way to Australia before joining the army.
James Mason plays Erwin Rommel once again, only two years after he had starred as Erwin Rommel in The Desert Fox. However, despite being billed second on the posters, Mason only appears in a couple of scenes. He's much more villainous in this film too - the film was made in part because people complained The Desert Fox had made Rommel too sympathetic.
- Affably Evil: Rommel, who treats MacRoberts like an officer and a gentleman but makes no bones about how he'll crush Tobruk and Germany will bring England to its knees. Mason's more villainous performance in this film was due to the backlash that followed after he portrayed Rommel as a straight-up hero in The Desert Fox.
- The Alcoholic: Bartlett admits that he lost his job in England due to drinking, and only joined the army in Australia when he was drunk in a bar. He's drunk when the company first musters for MacRoberts, and carries liquor around in his canteen.
- Artistic License – History:
- Strictly speaking the 9th Australian Division are called "The Rats of Tobruk", and the "Desert Rats" are the unrelated British 7th Armoured Division. The film was called The Desert Rats to echo The Desert Fox.
- The real Rats only had Australian officers at Tobruk, and Rommel wouldn't become a Field Marshal for another year.
- There is no depiction of the Polish riflemen, the Indian motor brigade or the British artillerymen that also held Tobruk with the Australians.
- Call-Back: When Lt. Carstairs leaves his position in the line to rescue their wounded captain, MacRoberts files papers to court-martial him but is talked out of it. Later MacRoberts lingers behind in an attempt to rescue a mortally wounded Carstairs, and as a result is captured by the Germans.
- Contrived Coincidence: Bartlett emigrates literally halfway around the world but still manages to find himself in an army unit commanded by one of his old students.
- Everybody Calls Him "Barkeep": Well, only one person, Bartlett, calls MacRoberts "Tammy". But we never do find out what MacRoberts's real first name is.
- Fatal Family Photo: Averted, surprisingly. MacRoberts busts out a photo of his wife and even tells Bartlett that he has a little son in England he's never seen. Somehow he makes it to the end of the movie alive.
- Field Promotion: The commanding general says that this is one of the best parts of his job, before promoting a bunch of officers, including MacRoberts to major.
- Last Stand: Until they hear the bagpipes, knowing the Big Damn Heroes arrive to relieve them.
- No Name Given: The anonymous British general in command at Tobruk, who appears to be an Expy of the real General Leslie Morshead.
- Plunger Detonator: The raid on the German ammo dump nearly goes horribly wrong when the Aussie soldier charged with pushing the plunger detonator is shot dead before he gets the chance. MacRoberts has to leap out of the truck and do it himself.
- Reality Has No Subtitles: This was pretty common practice throughout the studio era, actually. All the German dialogue is un-subtitled, although it helps when they use words like "sandstorm" and "Geneva Convention".
- The Siege: The epic eight-month Australian defense of Tobruk. The film does not deign to mention that barely six months later, during his second desert offensive, Rommel captured Tobruk with ease, 35,000 Commonwealth soldiers hardly firing a shot.
- Stock Footage: Some of the combat action, like a British pilot pushing the button on his machine gun.
- That's What I Would Do: The British general, when asks why he thinks Rommel will attack during the sandstorm, says "Wouldn't you?"
- Title Drop: "Come out of your holes, you desert rats!" says MacRoberts during the climactic charge.
- Villain Opening Scene: Opens with Rommel and his officer plotting an assault on Tobruk.