Here’s some not so sophisticated, but still deadly serious, military technology we discovered while walking along the river bank this morning.

Thankfully it never happened, but in 1940 there was every expectation that Britain would be invaded by Germany.  One preparation for that was the building of a series of defensive lines around London and other areas of the country.

The example here is a road block designed to slow down tanks and other armoured vehicles as they progressed in expected Blitzkrieg fashion across the green and pleasant land.  The concrete cubes extend down to the water’s edge, leaving a small gap that could be plugged with a removable barrier, possibly a duplicate of the piece of bent railway track, or hairpin, still in place.

I did a bit of fishing around, and discovered this particular defensive position close to Sunbury-on-Thames was part of the Outer London Stop Line.  Other types of defense included concrete pillboxes, minefields and trenches, plus use of natural features like the river here.

A road block like this one would likely be defended by another firing position nearby, so it wasn’t just a case of the enemy turning up and spending five minutes pulling out the barriers.

There are many similar features around UK, but I don’t think the seriousness of the threat at the time, or the extent of the defenses put in place to counter it, are widely known.

It’s also sobering to think these blocks were put down only 22 years before I was born.

More on British anti-invasion preparations of Word War II here.