By this date in 1940, the Battle of France was clearly lost. British troops had been evacuated at Dunkirk by June 4. Large numbers of French soldiers had been killed or captured, the French Air Force had been largely crippled, German armored units were marauding across wide areas of France. Columns of refugees were blocking the roads, seriously interfering with military operations. The French government had evacuated Paris for Bordeaux, and on June 16 the combative Paul Reynaud resigned as premier, to be replaced by the aged Philippe Petain.
And by June 18, the cadets of the French Cavalry School at Saumur, in obedience to the orders of their Commandant, had taken position to defend the bridgeheads across the Loire. It was a military operation that had been the subject of war-game exercises at the school for years, but few had imagined it would ever be carried out in earnest. The 800 cadets and instructors were joined by 200 Algerian riflemen, by various units in the vicinity, and by volunteers whose units had disintegrated but who wished to continue fighting. Arrayed against this small and ill-equipped force would be the German First Cavalry Division—more than 10,000 men, well-equipped with tanks and artillery.
The German attack started just before midnight on June 18. The cadets and their associated units held out until late on June 20. French casualties were 79 killed and 47 wounded–one of those killed was the composer Jehan Alain. German casualties are estimated at 200-300.
The German commander, General Kurt Feldt, was very impressed by the tenacity of the French defense, and so indicated in his report. On July 2, someone in the German command structure–probably Feldt–decided that out of respect for their courage and sacrifice in the battle, the cadets would be allowed to leave the school and transit into the Unoccupied Zone, rather than being interned as prisoners of war. He advised them to get going quickly, before someone in higher authority could countermand his order.
The most comprehensive English-language source on the Battle of Saumur is the book For Honour Alone, by Roy Macnab.