- In order to guard against a German attempt to bring ships into the port two wooden trawlers were sunk in the mouth of the River Blyth soon after the outbreak of war, but by June 1940 the action of the sea broke them up.
- A Luftwaffe aerial photograph from autumn 1940 shows that by this time some kind of net obstruction had been placed across the river and by July 1941 an RAF photograph shows that a chain boom or heavy rope was in place. This boom could probably be lowered to allow the passage of small vessels.
Wartime RAF aerial photograph showing the entrance to the Blyth. A number of wartime defences are highlighted. The thin dark line across the river to the right of the boat is the boom (With permission of English Heritage (NMR) RAF Photography). Click here to view a larger image.
The mouth of the Blyth today, in 1940 a potential landing place for German troops. The wartime river boom was placed close to this point.