Explanation from original OP:
In June 1940, the Germans are blitzing through France, Pétain announced the armistice on the 17th, and everyone thinks it's game over. Meanwhile in Saumur, a bunch of kids barely 20 years old – cadet officers from the Cavalry and Train School, 2,500 in total and poorly equipped – decide not to give up. Under Colonel Michon's orders, they spread out over 40 km between Gennes and Montsoreau, mine the bridges, and gear up to block the invaders' path.
On June 19, the German vanguard from the 1st Cavalry Division, led by General Feldt, rolls in from the north with 40,000 troops, 300 guns, and tanks. The cadets, packing training rifles and a few machine guns, fight back like demons: they blow the north bridge at Saumur after torching 7 enemy panzers, hold Île Offard, and repel assaults at Montsoreau. Shots everywhere, shells and Stukas overhead, total chaos, but these rookies stall the offensive for two full days, saving thousands of panicking civilians.
On June 20-21 they surrender, but the Germans, blown away by their guts, dub them "Cadets of Saumur," give them full military honors, and let them head to the free zone with their weapons. Toll: 250 French killed/wounded. They were resistors even before de Gaulle's call.