"Sir! Sir! I've got a war-winning weapon, sir!"

"Good man! The Germans are sunbathing on the Channel coast, the Italians have invented a new cut of trouser, and the Kiwis are unusually keen to send us someone called Bob Semple. What is it?"

"Concrete lorry, sir."

These particular turkeys were designed by Charles Bernard Matthews, director of Concrete Limited.

And I've got to hand it to him - it doesn't take an expert to realise that the Bison armoured truck fulfilled the brief. It was indeed both concrete *and* limited.

Regardless of the fact that a concrete manufacturer had certain conflicts of interest going on here, the ministry snapped them up. After all, there was also a conflict of, er, conflict going on and the British Army had left most of its tanks inconveniently parked in France.

It's important to note that Bisons were not armoured fighting vehicles. Nobody was expected to roll into battle in one.

The intention was to create a pillbox that could be moved onto airfields to defend them from lightly armed paratroops, a task they performed adequately.

Bisons were built on top of any chassis that came to hand, usually clapped out trucks that were otherwise useless for the war effort. The top speed was naturally of interest only to geologists, but the intention was to tow them onto airfields once invasion threatened.

Amongst the best donor vehicles were steam wagons, which coped well with the extra weight once the pistons and boiler were removed.

I should imagine it did nothing for the acceleration though...

Anything up to 300 of these things were made, or possibly poured, and a couple survive into museums - or at least the otherwise useless concrete part did, allowing recreations to be made.

And they stand as a memorial to quite how desperate the situation was when they were built.

PS - Charles Matthews' other great idea to expand his business, if not the hopes of an ungrateful nation, was giant pre-cast concrete spheres to help protect air raid shelters.

The fact I can't find any photos suggests the idea might indeed have been a load of balls.