Factual error: When Bruno is on his way to Union Station, he's heading on a bridge away from the Lincoln Memorial, which means he's leaving Washington D.C. for Arlington, Virginia, or in other words, he's going the wrong way.
Visible crew/equipment: When Gort picks up Patricia Neal next to the flying saucer, you can see cables leading down to her body to keep her hoisted. (01:20:15)
Continuity mistake: When the quake starts, Joyce Hendron runs to the arms of David Randall for protection. Ten seconds later, she again runs again to his arms. (00:41:55)
Factual error: When the Reindeer aircraft is on the ground at Gander, Jimmy Stewart pulls the landing gear handle, but only the left main gear folds up. All three landing gear (left, right, and nose) would have folded together.