These women are working on the Churchill tank, a World War two era British tank
that was heavily armored, but agile enough to climb. From 1941 to 1945 thousands
of what The New York Times called the "world's deadliest tanks" were made.
But there was a problem: the Churchill tank weighed at least 40 tons, 36 metric tons.
Imagine 20 cars. That would cause a normal bridge
to buckle without a way to cross water, the Churchill tank was basically useless.
American tanks had the same problem. And as the war waged on, the allies needed new bridges and
replacement ones. Bombed out bridges like this one in Germany needed a sturdier fix than a gangway.
The solution to both of these problems was a new type of bridge that improved on old breakthroughs
and also represented a model maker's way of thinking about how a bridge could win a war.
Here's a bridge being built in China in 2020. Now imagine no heavy machinery, no custom design, no
materials heavier than a person could carry, and no reliable access to the other side of the river.
And half the time, you had to build it at night. That's the challenge of a wartime bridge.
Donald Bailey was an engineer at the British Experimental Bridging Establishment in 1940,
and he needed a way to make the standard temporary bridge,
the Inglis bridge work for a new generation of heavy tanks. When the Inglis bridge buckled
under test weights, Bailey took an envelope out and sketched an idea for a new bridge.
He had made models since he was a kid and used them to help test his design. He needed something
adjustable to a range of gaps. It could work with a pontoon floating in a river
as well as with land. It had to be made of something other than aluminum
because airplanes needed that. It could be made easily by manufacturers. No confusing parts,
but most importantly, everything had to fit in a small service truck and be lifted by six soldiers.
The design is strong and more flexible than earlier ones like the Inglis Bridge
or this small box girder bridge that was also used. The panel was smaller
than a box girder, lighter and easier to stack. This is the key to his design. I'll show you.
It's the real breakthrough ingredient. This reinforcement makes a bridge that's really strong,
but at just five hundred and seventy pounds or two hundred and fifty kilograms, six
people could lift it. Other designs like the Inglis bridge, twisted under heavy weight.
The Bailey Bridge didn't. You can see how easy it is to move in
this video made shortly after the war. Panels were joined by pins driven in. After that, soldiers
laid a transom across. I used glue to join mine, but clamps made the process even easier.
But it is the next step, before finishing the bridge,
that made the Bailey Bridge even more special. See these men pushing? You could roll a Bailey
Bridge across a gap—important when you couldn't get to the other side during a war.
I can kind of show you with mine and this roller right here.
Rollers to slide the bridge alone and a link to make the front of the bridge
slightly tilt up by making the bottom longer than the top. You can see it here in this Army manual.
The bridge is pushed along the rollers with more weight, usually more panels in the back
to keep it from tipping over. Sometimes they drive on it as a counterweight too.
In the front, this link makes the nose tilt up. The snoot didn't droop.
That helps keep it from sinking into the gap as it gets pushed across.
Adding a second or even third level was easy, thanks to the Bailey Bridge's modular design.
These bridges quickly became an indispensable tactical trend.
By 1943, wartime manuals were sandwiching crucial Bailey Bridge facts
in between information about German guns and warnings about dangerous fish.
The Allies built twenty five hundred Bailey Bridges in Italy and fifteen hundred in
northwest Europe, as well as some in other theaters, allowing those heavy Churchill tanks
and the American equivalents to move over land and water alike.
General Dwight D. Eisenhower said, "along with radar and the heavy bomber,
it was one of the three most important engineering and technological developments of World War II."
Now, labeling the Bailey Bridge as the reason the Allies won the war,
it's impossible to say. However, a model maker's breakthrough gave them a tool that was flexible,
fast and strong in a war that needed all three of those things.
The modular design presaged a more flexible, nimble type of construction.
And the Bailey Bridge did allow them to cross the rivers in Italy and push a bridge over the Rhine.
They could use a Bailey Bridge, playing accordion
over the water. And
they could cross and play piano amidst the ruins.