Today is the seventieth anniversary of the D-Day, which began the Allied invasion of Nazi-occupied France. D-Day (or "Operation Overlord" to use its official title) was a herculean planning task, requiring remarkable coordination both between the British, American, Free French, and Commonwealth armies, and with French resistance fighters on the ground, who were charged with helping aerial bombers disrupt German transportation routes, so as to impair the Germans' ability to send reinforcements.
One of my favorite details of the whole plan was how the Allies alerted the French that it was time to begin sabotaging rail-lines: they had the BBC broadcast lines from Paul Verlaine's poem "Chanson d'automne." On June 1, to tell the resistance to stand by for further alerts, the BBC transmitted the first three lines:
Les sanglots longs
Per Arthur Symons' translation: "When a sighing begins / In the violins / Of the autumn-song".
"The Germans wrongly believed that these lines were addressed to all Resistance circuits in France, and that when the next three lines were broadcast it would mean that invasion would follow within forty-eight hours," Martin Gilbert writes in his history of D-Day. "The lines were directed to a single Resistance circuit, Ventriloquist, working south of Orléans, instructing it to stand by for the next three lines, which would be the signal for it to carry out its railway-cutting tasks — in conjunction with the Allied landings."
Then, on June 5, to signal that sabotage efforts should begin, the next three lines were sent:
Blessent mon coeur
Symons: "My heart is drowned / In the slow sound / Languorous and long."
Both lines were intercepted by German forces, who took them as significant but didn't take adequate action; for one thing, they overestimated the scope of the sabotage operations to come. Gilbert explains:
The second three lines of the Verlaine poem…were broadcast over the BBC to the Ventriloquist Resistance circuit, instructing it to act at once in carrying out its railway-cutting sabotage. The SS Security Service radio interception section in Paris heard this as it was broadcast.
Believing, rightly, that the broadcast of the section section of the poem was related to invasion, but wrongly, that it was an Allied call for railway sabotage throughout France, the Security Service immediately alerted the German High Command in the West.
An hour later, the German Fifteenth Army warned its various corps that intercepted messaged pointed to an invasion within forty-eight hours (the parachute landings were fewer than three hours away). The German force responsible for most of the imminent assault area, the Seventh Army, which had received too many false warnings in the past, took no action.
The combination of airstrikes and ground sabotage proved extremely successful, especially as they wound up forcing the Germans to cross the Seine via ferry; as Mississippi State historian Mary Barbier writes in her history of D-Day, the Germans ended up sending two panzer divisions all the way from the Russian front to fend off the invasion, but because of sabotage and bombings, "it took less time…to travel from the eastern front to France than it did for them to proceed from eastern France to Normandy."