The film opens with the U.S. Army failing to capture the still-intact Oberkassel railway bridge. Lieutenant Hartman (George Segal) is an experienced combat team leader who is becoming weary of the war in Europe. After he is promoted to company commander following the reckless death of the previous officer, Hartman is ordered to advance to the Rhine River at Remagen where he is promised a rest for his men. At the same time, Major Paul Kreuger (Robert Vaughn) of the Wehrmacht is tasked with destroying the Remagen bridge by his friend and superior, Colonel General von Brock (Peter van Eyck), who has been given a written order to do it immediately. The general appeals to Kreuger’s sense of honor, giving him a verbal command to defend the bridge for as long as possible, to allow the 15th Army trapped on the west bank of the river to escape.
After capturing the undefended town of Meckenheim, four miles from Remagen, Hartman is ordered by his battalion commander, Major Barnes (Bradford Dillman), to continue the advance until encountering resistance. Kreuger tours the defences above the town of Remagen and assures the handful of troops, which are just old men and boys, that the general personally guaranteed tank reserves are on the way. When Hartman’s troops attack the town, Kreuger is shown the reality when he calls for the promised tanks and is told they have been sent “elsewhere”.
On finding the bridge intact, General Shinner (E. G. Marshall) orders Major Barnes to secure its capture, saying: “It’s a crap shoot, Major. We’re risking one hundred men, but you may save ten thousand”. Barnes agrees to send in Hartman’s company, and orders the troops to gain a foothold across the Rhine River, thus avoiding a costly assault-crossing elsewhere. Sergeant Angelo (Ben Gazzara), one of Hartman’s squad leaders and friends strikes Barnes after the Major threatens Hartman.
As the American soldiers rush the bridge, Kreuger, along with explosives engineer Captain Baumann (Joachim Hansen) and Captain Schmidt (Hans Christian Blech) from the Remagen Bridge Security Command, try to blow up the bridge, but the explosives they use prove to be not the high-yield military grade charges needed for the job, but weaker, industrial explosives, which fail to destroy the structure. Hartman’s troops dig in to consolidate their hold on the bridge.
Kreuger shoots two soldiers as they try to desert. Realising the futility of the situation, Kreuger returns to HQ to make a personal appeal to the general for more reinforcements, but on arrival finds that building taken over by the SS. Von Brock has been arrested for being “defeatist”. Kreuger is questioned about the delay to blow up the bridge and arrested.
At Remagen, Hartman leads a raid against a machine gun nest installed by Kreuger on board a barge moored to the bridge, but while taking its crew out, Angelo is hit and falls into the river. Hartman marches on foot towards the bridge defenders’ post at the same time as a squadron of M24 Chaffee light tanks cross the bridge. The remaining German soldiers surrender to the Americans. In the aftermath of the battle, Hartman discovers Angelo alive. The next day, Kreuger is led out for execution by an SS firing squad. With the sound of airplanes overhead, Kreuger asks: “Ours or theirs?”. The SS attending officer replies, “Enemy planes, sir!” “But who is the enemy?” muses Kreuger before he is shot.
A screen crawl informs the viewer that the actual structure collapsed into the Rhine ten days after its capture.