During a thunderstorm in early September 1944, units of the 35th Infantry Division are nearing the French town of Nancy. One of the division’s mechanized reconnaissance platoons is ordered to hold their position when the Germans counterattack. The outnumbered platoon also receives friendly fire from their own mortars.
Private Kelly (Clint Eastwood), a former Lieutenant scapegoated for a failed infantry assault, captures Colonel Dankhopf of Wehrmacht Intelligence. Interrogating his prisoner, Kelly notices the officer’s briefcase has several gold bars disguised under lead plating. Curious, he gets the colonel drunk and learns that there is a cache of 14,000 gold bars, worth US$16 million ($230 million today), stored in a bank vault 30 miles (50 km) behind enemy lines in the town of Clermont. When their position is overrun and the Americans pull back, a Tiger I kills Dankhopf.
Kelly decides to go after the gold. He recruits Supply Sergeant “Crapgame” (Don Rickles) in order to obtain the supplies and guns that will be needed. A spaced-out tank platoon commander known as “Oddball” (Donald Sutherland) overhears, and he and his three M4 Sherman tanks join the caper. With their commanding officer, Captain Maitland (Hal Buckley), preoccupied pursuing opportunities to enrich himself, the men of Kelly’s platoon are all eager to join him. After much argument, Kelly finally persuades cynical Master Sergeant “Big Joe” (Telly Savalas) to go along.
Kelly decides that his infantrymen and Oddball’s tanks will proceed separately and meet near Clermont. The Shermans fight their way through the German lines, destroying a railway depot in the process, but the bridge they need to cross is blown up by Allied fighter-bombers. Oddball contacts an engineer unit to build him a bridge, and the engineers in turn bring in even more men for support.
After losing their jeeps and halftracks to friendly fire from an American plane that mistakes them for the enemy, Kelly and the others proceed on foot and unknowingly walk into a minefield. Private Grace is killed when he steps on a mine, and PFC Mitchell and Corporal Job are killed when the men are forced to engage a German patrol.
Oddball links up with Kelly two nights later, bringing with him the extra troops. They battle their way across the river to Clermont. By this time, intercepted radio messages attract the notice of the 35th Infantry Division commander, Major General Colt, who misinterprets them as the efforts of aggressive patrols pushing forward on their own initiative. He immediately rushes to the front to exploit the “breakthrough.”
Kelly’s men find Clermont defended by three Tiger tanks of the 1st SS Panzer Division with infantry support. The Americans are able to eliminate the German infantry and two of the Tigers, but the final tank parks itself right in front of the bank and Oddball’s last Sherman breaks down, leaving them stalemated. At Crapgame’s suggestion, Kelly, Big Joe, and Oddball approach the Tiger and offer the commander and his crew a share of the loot.
After the Tiger blows the bank doors open, the Germans and Americans divide the spoils – worth US$875,000 each ($10 million today) – and go their separate ways, just barely ahead of the still-oblivious General Colt, who is blocked from entering Clermont by the French residents, who have been deceived by Big Joe into thinking that Colt is Charles de Gaulle.