I'm looking for a movie, I think, about World War

It is the steadfastness of soldiers in a warehouse or building, and on top of the building there is a flag, and there is a plane that shoots them, and there is also a bridge opposite the building that reaches a peaceful city in which there is no war, and whoever tries to cross the bridge is thrown, and between the two cities there is water, and there are some soldiers trying to sneak in at night to cross the other bank