The Outer London Stop Line
|A type 24 pillbox just off Swanley Bar Lane in the fields of the Royal Veterinary College|
Image from Jim Apps
In 1940, as the German army swept across mainland Europe to the shores of France, Britain was in imminent danger of invasion. Only the English Channel stood in the enemy's way.
As the Germans occupied France, Norway and the low countries, the length of our shoreline that had to be defended increased dramatically. The fixed lines of defences, built to prevent invasion from the sea, were known as the General Headquarters (GHQ) Lines.
Behind the coast, the threat of airborne landings required the guarding of more than 1,500 vulnerable points, such as airfields, army establishments and centres of military production.
By far the most vulnerable area, and the most important target for the German Army, was London. To prevent the capture of London and everything it contained, a fixed ring of anti-tank ditches and pillboxes were built as a final line of defence. This was known as the outer London stop line.
This line passed through the southern part of Hertfordshire, from Watford to Cheshunt, and much of it still remains today.
|Type 24 pillbox with what could be the remains of the stop line anti-tank ditch running east|
Image courtesy of Jim Apps
My research has shown that not a lot has been written about this important part of our history, although the positions of the pillboxes have been recorded by various organisations such as Hertfordshire County Council and the Defence of Britain Project.
By building the website, Fortress Hertfordshire, I am attempting to make some of our important historical structures available to a wider audience.
The site has 40 images of tanks traps and pillboxes in Northaw, Cuffley, Potters Bar and Watford, along with information explaining their importance to the defence of Britain.
For example, on the north side of the Ridgeway in Northaw, to the west of the Great Wood, is a pillbox. Opposite it, on the south side of the road, is a set of anti-tank blocks.
In front of the pillbox are the remains of the anti-tank ditch. This would have formed part of a roadblock.
|A tank trap just off Swanley Bar Lane|
Image courtesy of Jim Apps
Close to another pillbox in Northaw is an ammunition store used by the Home Guard to store self-igniting phosphorous anti-tank grenades or explosives.
One of the picture on Fortress Hertfordshire shows the remains of what is thought to be a store for damp-sensitive items such as fuses. These stores are unusual in Hertfordshire.
Also, on the east side of Great Woods is a short length of concrete roadway, believed to have been the access to an anti-aircraft emplacement.
About 100 yards from the Ridgeway's junction with Carbone Hill there are four anti-tank blocks, two on either side.
Between these blocks, set into the road, are five rows of sockets into which steel rails could be placed, standing upright, to prevent tank access.
Three of these rows still contain the original metal sockets. This type of roadblock is unique in the county.
© Jim Apps 2003
Editor's Note: Former local resident Jim Apps carried out the research for Fortress Hertfordshire while living in the area. After he retired he moved to Devon, but he still retains a keen interest in the outer London stop line. He wrote this piece in 2003. You can read more about local defences in an article on this site about North Mymms tank traps, and another article about a local spigot mortar emplacement. There are more articles about the war years, including a feature on the North Mymms Rifle Range, a POW camp in Welham Green, and a booklet about life 'On The Home Front' in North Mymms during the war years. There is also a feature about young evacuees from London being sent to live in Brookmans Park.