Goofs

When Angus first takes the egg into the workshop, you can see the door to the workshop is set in a recessed porch and it is cloudy. The next shot, as he enters the workshop, has the sun streaming through the glass in the door. Whilst it is feasible that the sun could have just come out, it would be impossible for it to be streaming through the glass, given the position of the door in the previous shot.

When the fishermen "catch" Crusoe, the condition of the loch's surface varies between flat to slightly choppy in different shots.

Loch Ness is depicted as opening almost directly into the sea (hence the subplot about Crusoe being mistaken for a U-Boat). In reality, Loch Ness is five miles inland and eighty feet above sea level, the only access to the sea being the shallow River Ness, making it impossible for a U-Boat to enter the loch.

Had Angus spent a prolonged period immersed in the water in real life, he'd be courting hypothermia in short order, given that the Loch is notoriously cold.

The water is depicted as being crystal clear when Crusoe takes Angus on a ride. In reality, the water of Loch Ness has a high concentration of peat, which makes it murky and almost opaque beyond just a few meters.

When the fisherman hooks Crusoe, Crusoe pulls his boat along. The fisherman wasn't fastened in, so he should have been pulled overboard.

When Angus's mum is looking at Angus, Gracie and Hughie through a window in the door, the camera seems to just see them through the window, but when we see Angus's mum looking through the window, the window is obscured or cracked.

The net that is installed to catch the submarines on the lake is made of metal, in the close view and you can even hear the sound of metal rods colliding with each other; but in the wide view of the net, it looks a net made of rope which moves with wind and waves.

The British forces stationed on the estate are using U.S. military vehicles. These would have not been available to them until after the war ended and left there as surplus.

In an early scene, Angus pulls out a first aid kit, and the bandage on top is labeled 'Telfa'. The film is set in 1942, but Telfa bandages weren't marketed by the Kendall Company/Curity until 1954.

The famous "Surgeon's Photo" of a monster in Loch Ness, published in newspapers around the world in 1934, plays an important part in this story, where it is claimed to be first created in 1942.

When the Hawker Hurricane flies over the Loch, one of the wings is painted black. Originally designed to make the Hurricane easily identifiable by the anti-aircraft gunners, this color scheme was definitively abandoned in 1941, one year before the story is supposed to happen.

In the workshop, Angus has a toy ship which is clearly seen and is the SS America - this ship was only launched 1940 and would have been relatively unknown in Europe.

The film portrays Loch Ness as having direct access to the sea (so much so that anti- submarine nets are necessary). In truth it is 10 miles from the sea along the River Ness in the north, and around 30 miles along the Caledonian Canal to the south. Along that length there are 29 locks which would also prevent submarines (or sea monsters) travelling from the sea into the loch.