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At 7.15 am, 23 March 1918, there was an explosion in the Place de la République; a second, fifteen minutes later in the Rue Charles V; and a third, in the Boulevard de Strasbourg. No warning had been given by the listening posts to the north of Paris, and civilians and airmen alike scanned the skies in vain for German bombers. Only by reassembling the fragments did the French work out that they were dealing with artillery and not aircraft. Over the next twenty-four hours, a total of twenty-one shells landed in the city itself, and one in Châtillon. Yet such a solution seemed incredible. René Fonck (SPA103) was at the front that day. 'We received a telephone message during the afternoon telling us they were shelling Paris,' he recalled. 'The news seemed so implausible that everyone burst out laughing. I preferred to keep my own counsel. How could a gun sited more than 120 kilometres away drop a shell close to the Gare de l'Est? Everyone thought the idea quite frankly ridiculous. But then how could aircraft possibly conduct a daylight raid, pass unseen through a swarm of SPADs all positioned to stop them, and drop bombs all morning? The gun hypothesis offered the only possible explanation. Only the range remained a mystery.'
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to avoid them. My observer began taking photographs. Now we were over Crépy, the batteries still going hammer and tongs. The SPADs never left me for an instant. At one point they dived across me towards six German fighters. The [Boches] shot down one of our chaps, then headed towards Marie. Someone came spinning down. A Boche or a Frenchman? I got my answer five minutes later [when] just three SPADs followed me across our lines. I hoped our comrade had only been wounded. The mission was over: I was first to land, and as each aircraft followed we all ran over in search of news. Once we were all down, we found out the missing pilot was Lieutenant Lecoq. We later discovered he'd been the one shot down by the six Boches over our lines. He'd taken a number of hits to the body. Although our photos weren't great, they did show the exact location of the “Berthas”, so we could start correcting the fire of the guns detailed to destroy the enemy “colossi”.
During the flight, my colleague Adjudant [Charles] Quette spotted a flash that proved to be the firing of one of the Crépy guns. A few days later, new photographs were deemed necessary to supplement the information we'd gathered during our first trip and to confirm the effects of our fire. I was picked again, with Lieutenant [Paul] Brousse as my observer. A second crew accompanied us: Adjudant Fabien Lambert (pilot) and Lieutenant [Robert] des Allées (observer). Despite adverse weather conditions, sustained and accurate anti-aircraft fire and the continual presence of enemy fighters, we got [our] new photographs.'
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In terms of actual damage caused, the effect of the guns was negligible - the shells were too small for that. The real target of the guns was always intended to be French civilian morale - demonstrating that Paris was not safe even though the Germans were 75km away.
There is a bit of a mash-up of a video on YouTube here.
Pictures: one of the guns firing during its trials; one of the reconnaissance photos of Crépy-en-Laonnois, with the gun sites ringed (Albin Denis); a SPAD 11; the damage done to the church of Saint-Gervais-et-Saint-Protais (Gallica); the crews of BR213, tasked with spotting for the French batteries (from La Guerre Aérienne Illustrée)