Since 20 June, 2nd Company, 189 Fortress Alpine Battalion (BAF), with a 47mm anti-tank gun, had controlled the left bank outlet of the viaduct from the Mollard de Vions hill, which overlooked the railway, the village of Vions and the road leading to La Loi.
Two trains were derailed on the viaduct.
The Alpine infantrymen, who had been on the alert since the attack on the road bridge on 22 June morning, sent reinforcements to the defenders of La Loi in the morning.
At noon, an infiltration attempt from the right bank by German infantrymen was thrown back and, faced with the threat, decision was taken to blow up the viaduct, but the firing mechanism had disappeared and the viaduct remained intact.
At 1pm, German 2 Battalion crossed the La Loi bridge and entered the Savoie region to take the Vions viaduct defenders in the rear by the La Loi-Vions road.
Half of the defenders were captured, the others tried to join units of either Chanaz or Chindrieux.
At 2 pm, the viaduct was seized as well as the village of Vions, opening the road to Chanaz to the Germans.
As soon as it crossed La Loi bridge, enemy launched its 3 battalions towards the right bank of the Lac du Bourget.
Objective was to take Sapenay and Chambotte passes, in order to reach Annecy and Aix.
12th company, ID 145 set up strongpoints at the crossroads leading to the bridges on axis Ruffieux-Chindrieux to slow down the enemy in order to reinforce the defense of the passes.
The defenders held on to the ground despite German artillery, but to avoid being overrun, gradually withdrew to Ruffieux strongpoint, which fell in the afternoon.
At the end of the day, the German bridgehead held Chautagne as a whole and the two bridges.