WEBVTT
Kind: captions
Language: en

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This used to be RAF Graveley,
a Royal Air Force base near Cambridge.

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Now, it's a farm and some wind turbines,
but in the 1940s

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aircraft would set off from here
to fight in Europe.

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And, they hoped, they'd be able to safely
land back here as well.

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The problem with that was the fog.

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Or, rather, smog: all the soot and air pollution
from domestic coal fires

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combined with fog to make an incredibly thick
"pea soup".

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It's never seen in modern Britain

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because we don't burn smoke-producing coal
in every house any more.

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But back then, if that smog came in,

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even runway lights wouldn't get through it

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and there were no modern instruments
to guide the air crews home.

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No way to take off, no way to land.

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How do you solve that?

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By setting enormous amounts of petrol on fire.

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This incredible photo shows a Lancaster bomber
taking off from just behind me,

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more than 70 years ago.

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It looks like a movie stunt,

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but this was how wartime airfields
boiled off fog.

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Set up enormous lines of petrol burners to
heat up the air,

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vaporise all the liquid water droplets to
make steam,

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which will rise out of the way
and clear the air.

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The system was called FIDO.

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“Fog, Intensive, Dispersal Of.”

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There are demonstration films taken by the
RAF on clear days,

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showing just how big
and how visible this was.

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There's a report in The War Illustrated,

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published just after victory in Europe,

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that says that the glow from the fires was
visible for miles.

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There was a bit of smoke
when they started the system up,

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but once it got hot, the air could be so clear

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that people on the ground could see the stars.

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The catch was how expensive it was.

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A small Fido system burne
70,000 gallons of fuel an hour.

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One estimate says that in one foggy night
over England,

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all the Fido systems in use
would burn 20 million gallons of fuel.

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There's even a report all the extra heat pumped
into the atmosphere triggered a thunderstorm.

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At the current price of jet fuel,
as I record this,

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running a Fido system would cost
about $200,000 per hour per runway.

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It was never used in peacetime:

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aircraft could just not take off instead
and wait for the fog to clear,

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or divert to another airport if they were
trying to land.

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But for the war effort,

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to let planes take off for battle in any weather

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and to save thousands of air crew lives

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who needed to land right now:

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it was worth it.