When a group of American soldiers land on Omaha Beach during the D-Day invasion, Captain John Miller (Tom Hanks) leads them as they set up for an attack against the Germans. Their objective is to blow up a bridge referred to in the film as the Alamo, so that it can't be used by the enemy when they arrive on the scene.
The Alamo is a bridge that was rigged with explosives in order to blow it up if the Germans attempted to cross. However, this was a measure of last resort and it wasn't as important to the Americans as it was to the Germans.
In the movie, the American soldiers search a pile of dog tags that they've recovered from dead soldiers and are told that Private Ryan may be one of them. But they are reprimanded by Wade, their squad leader, who tells them that they're acting callously when they scour the dog tags.
Another soldier explains to the group that Ryan was assigned to guard a critical bridge in Ramelle, a town that lies near Omaha Beach. But he was reassigned due to his unit's commanding officer being killed.
The soldier also tells the group that the bridge was rigged with enough TNT to blow it up if the Germans tried to cross. This was a strategy that they used in order to keep the Germans from reaching their objectives and making them more likely to lose control of Ramelle.