Goofs

When the group converges to dig Basil Brown out of the collapsed mound, the soil they are digging in is significantly damp. But in the very next shot, where Basil is seen from above, the soil is bone dry, and significantly lighter in colour.

When Ralph Fiennes's character Basil Brown is buried under the excavation, Carey Mulligan's character Ms Pretty along with others rush in to dig him out. The mud that fell on Mr Brown was actually loose from having dug up. But the rescuers are shown trying to dig through heavily compacted mud instead.

Basil Brown tells Mrs Pretty ''that's a partial eclipse of the moon'' before the actual eclipse took place several months later at the end of October 1939.

When Mr Brown is buried by the cave in Mrs Pretty performs "mouth to mouth" resuscitation. 13 years before Professor Peter Baskett demonstrated it and CPR for the first time.

When Edith Pretty is departing in the car there are newspaper photographers all around the vehicle snapping photos using flash photography. But it's broad daylight so no need to use flash. This is a device used in film to inform the viewer that photos are being taken but in reality wholly unneeded.

In fact there are several reasons to use flash with open light. One of them is to freeze movement. This was very important in the old days, when film had a very low ISO and pictures needed long exposure times. So if you wanted to photograph subjects in movement, firing a flash was very useful. However, in the 1930's British press photographers would already be using Ilford FP or HP film, both of which were fast enough to not require flash in broad daylight. Another reason to nevertheless use flash would be to reduce the shadow cast by e.g. the brim of a hat.

When the plane crashes into the river the cast follow the trajectory of the plane over the trees. Upon discovering the crash site Rory dives in behind the plane and discovers the plane head on, instead of its tail end.

However, when the plane hit the water, and subsequently sank, it could have spun or twisted before settling on the bottom of the river, so it could have ended-up in any conceivable position.

Edith's son Robert can be seen wearing an aluminium foil hat early in the movie, Aluminium foil did not surface until after the war, but tin foil had existed since the 19th century.

In one scene, set in 1939, when the butler is asked to switch the house radio on the sound comes through immediately. However practically all mains valve radios from the late 1930s onward were slow to reach emission temperature, with wait times routinely exceeding 10 seconds before audible sound was produced. It was not until transistor radios were developed in the 1950s to replace valves that warming up time was eliminated.

In the garden party scene near the end, Ralph Fiennes' character mentions "Lemon drizzle cake." According to the Oxford English Dictionary this term was first recorded in 1969.

The excavation is being done with 5 Gallon plastic cans, which were first used in the late 1940s.

Mrs Pretty performs mouth to mouth resuscitation on Mr Brown - historically it was only developed about 2 decades after the dig.

Long shot towards end of the view across the dig field showed very high, jagged hills in the background. No hills like that in view of Sutton Hoo.

A war plane is seen from the dig site to sputter out and crash in the English Channel. Rory runs what Google Maps shows to be 5+ miles, dives in the water, and the plane is still sinking. The screenplay and producers must have taken liberties.

Addendum - It's not the English Channel. Sutton Hoo is in Suffolk (near Woodbridge). If this is a factual event, the plane must have crashed in the River Deben as that's the only major waterway within walking (or running!) distance of Sutton Hoo.