Goofs

Sailors marching away from car which has run out of gas are without weapons, but shortly after, they are in hand.

Some of the clothing Mrs. Whittaker removed from the clothesline is back there later when Kolchin returns to the house.

The interior sets for the Russian submarine are way more roomy and comfortable than real non-nuclear submarines of the era.

Chief Mattocks is riding in a police Jeep with flashing red emergency lights. Police vehicles in Massachusetts use only blue emergency lights.

Established etiquette for displaying the United States flag when hung vertically is to have the blue union on the uppermost left - during the credits at the end of the movie the flag appears with the union on the upper right.

When Police Chief Mattocks "breaks" Fendall Hawkins' sword over his knee, it doesn't break on the first try (hit between his hands), but half the sword can be seen flopping around outside Mattocks' right hand. It is possible either that the sword was already pre-broken/weakened in that spot, and Brian Keith "missed the mark", or that he broke it once in a previous take, but had to do a retake, and needed to "hide" the first break.

When Luther Grilk connects with his horse, Beatrice, it is immediately apparent that "she" is a stallion.

In several scenes the sub is shown "grounded" on the island, but in those same scenes, the sub is "rocking" with the motion of the waves. Beached vessels are solidly grounded and do not move.

The Russian submarine has a deck-mounted gun which figures prominently in the standoff in the harbor. The last Soviet submarines with such weapons were the K-class built during World War 2 and the last surviving example of the class was K-56 which was sunk in a nuclear weapon test in 1957.

Just after his sword is broken by Chief Mattocks, Fendall, whose back is to the camera, is clearly saying something, but the soundtrack has been wiped.

As the flotilla of small boats moves away from the docks, registration numbers can be seen on their bows. Most of the registration numbers start with CF (California), even though Gloucester Island is in Massachusetts.

The setting of the story is an island off of New England, but the igneous rock formations on the beaches in the first and last coastal scenes identify the location as part of the volcanic ring of fire, which the eastern seaboard does not have.

Based on the position of the sun and shadows, the "West side" of the island (including West Village) is on the east side of the island.

When the Whittakers are eating breakfast under the supervision of Kolchin, Mrs. Whittaker pours a cup of milk from a carton with a large letter "f" on it, which is the logo for Foremost Milk. This brand was only available on the west coast and not in Massachusetts.

When Alice first calls the police chief with Muriel's report of the Russians, she never mentions West Village to the chief. Later, the chief repeats what Alice told him, but inserted West Village - information Alice never told him.

At two different times both Rozanov and the Captain are at a loss to pronounce "Gloucester", but early in the film it is shown to be "Gloster" on their chart, in very large Cyrillic letters.