Continuity mistake: During the final attack the cloud cover is continuously changing. One minute it's clear, than over cast, then wispy cirrus clouds, then puffy cumulous clouds all between shots. (01:13:00)
Continuity mistake: In the underground bunker Carol and Dr. Marvin listen to the aliens voice from the slowed down tape recorder. At first we see the tape in the middle of the spool than ten seconds later it jumps to the end. (00:25:45)
Visible crew/equipment: When seen up close the aliens helmets have no openings. When the alien spaceship takes off outside the Belmont lab one of them is left inside. As he walks out the reflection of the window on the front of his helmet and the person in side can be seen in the sunlight. (00:54:20)
Audio problem: As the aliens announce their intentions to the people of earth Dr. Marvin walks up to a television set in the back of the lab and turns it on. We hear the over-dub of the aliens speaking through the television set but it's obvious that the unit never comes on. (01:04:55)
Visible crew/equipment: As the alien spaceship rips apart the Washington monument, two shots later it falls to the ground and the bricks are not the right size and the wires holding them can be seen. (01:18:20)
Continuity mistake: Carol and Dr. Marvin stand in the front of the Supreme Court Building as the aliens destroy it. As they cut away to the long shots of the front of the building they're not there but then in the close-ups they are. (01:19:05)
Deliberate mistake: After the aliens announce their intentions Dr. Marvin meets with Carol back at their hotel room. He tells her that she must take a flight alone back to Palm Springs and then leaves the room. In the end of the scene she picks up a copy of The Evening Star, which is an obvious prop as it has no date on it. (01:08:50)
Plot hole: After being denied permission to contact the aliens by himself, Dr. Marvin returns to his hotel and calls them up on the radio anyway and arranges to meet, despite not being allowed to leave the hotel. His wife says she overheard him say he's under orders not to leave and begs him to call someone instead: "Call Huglin". She shouldn't know who Huglin is because Huglin was only assigned to guard them as Marvin was being denied permission to contact the aliens.
Continuity mistake: After the general says, "I'll show you how it works" they all turn and follow him. In the next shot they're in an entirely different room. (01:00:55)
Visible crew/equipment: As the saucer lands on the White House lawn a truck with the magnetic interference unit on it pulls up and you can see the reflection of the crew in the shiny driver's side door. (01:15:35)
Continuity mistake: After listening to the alien translating device from the helmet the general says, "I'll show you how it works" and Maj. Huglin turns to look at Carol twice between shots. (01:00:40)
Continuity mistake: As Prof. Kanter is incinerated by the alien's beam we can see the shadows cast by the leaves of the trees move before our eyes between shots. (00:55:00)
Visible crew/equipment: At "Operation Sky Hook" Dr. Marvin says to Carol, "I want you to transcribe these notes for my report" and you can see the shadow of the camera as it follows them on the left of the screen. (00:07:20 - 00:15:50)
Continuity mistake: When they remove the helmet from the dead alien the front of Dr. Marvin's hair is combed differently than it was earlier in the scene. Carol's hair changes also throughout this scene. (00:56:20)
Visible crew/equipment: In the final battle an alien spaceship rips apart the Washington Monument and if you look closely you can see cracks in the spot where it eventually breaks apart before we see it happen. (01:18:20)
Visible crew/equipment: A soldier on the truck with a magnetic interference unit on it says, "Dr. Marvin, Dr. Marvin, we've made contact with GHQ". The crew can be seen filming across the street in the reflection in the truck. (01:19:45)
Continuity mistake: At Carol's barbecue a soldier drives up in a jeep with a message for Dr. Marvin stating that they lost contact with rocket No. 11. Dr. Marvin holds the message and an envelope in his hand as they look up and see the rocket burning up in the atmosphere. He never puts the message back into the envelope but when he sits down the envelope is alone and the messages is gone. (00:13:50)
Continuity mistake: In their spaceship the aliens use the infinitely indexed memory bank beam to read Gen. Hanley's mind and his hair is combed and his face is dry. In the next shot his hair is messed up and his face is sweaty. (00:24:20)
Continuity mistake: When the Marvin's start necking as they drive to "Operation Sky Hook", the background we see through the rear window shows a curve, but Carol's hands on the steering wheel never move. (00:03:25)
Deliberate mistake: As the Marvin's approach "Operation Sky Hook" they hear the UFO above. Out the rear view window we can see the same sign and background they passed several minutes ago when the doctor started making his tape recording. (00:05:15)
