字幕表 動画を再生する 英語字幕をプリント This used to be RAF Graveley, a Royal Air Force base near Cambridge. Now, it's a farm and some wind turbines, but in the 1940s aircraft would set off from here to fight in Europe. And, they hoped, they'd be able to safely land back here as well. The problem with that was the fog. Or, rather, smog: all the soot and air pollution from domestic coal fires combined with fog to make an incredibly thick "pea soup". It's never seen in modern Britain because we don't burn smoke-producing coal in every house any more. But back then, if that smog came in, even runway lights wouldn't get through it and there were no modern instruments to guide the air crews home. No way to take off, no way to land. How do you solve that? By setting enormous amounts of petrol on fire. This incredible photo shows a Lancaster bomber taking off from just behind me, more than 70 years ago. It looks like a movie stunt, but this was how wartime airfields boiled off fog. Set up enormous lines of petrol burners to heat up the air, vaporise all the liquid water droplets to make steam, which will rise out of the way and clear the air. The system was called FIDO. “Fog, Intensive, Dispersal Of.” There are demonstration films taken by the RAF on clear days, showing just how big and how visible this was. There's a report in The War Illustrated, published just after victory in Europe, that says that the glow from the fires was visible for miles. There was a bit of smoke when they started the system up, but once it got hot, the air could be so clear that people on the ground could see the stars. The catch was how expensive it was. A small Fido system burne 70,000 gallons of fuel an hour. One estimate says that in one foggy night over England, all the Fido systems in use would burn 20 million gallons of fuel. There's even a report all the extra heat pumped into the atmosphere triggered a thunderstorm. At the current price of jet fuel, as I record this, running a Fido system would cost about $200,000 per hour per runway. It was never used in peacetime: aircraft could just not take off instead and wait for the fog to clear, or divert to another airport if they were trying to land. But for the war effort, to let planes take off for battle in any weather and to save thousands of air crew lives who needed to land right now: it was worth it.