The drive to the Seine began on 3 August, when General Bradley instructed Lieutenant General George S. Patton, one of the U.S. Army's greatest exponents of armored warfare, to secure the north-south line of the river Mayenne, clear the area west of the Mayenne as far south as the Loire, and protect the 12th Army Group south flank with minimum forces.

[7] In his order issued on 20 August, General Montgomery cautioned: "This is no time to relax, or to sit back and congratulate ourselves.

[9] The 79th was to get foot troops on the east bank at once, build a bridge for vehicles, tanks, and heavy equipment, and gain ground in sufficient depth (four to six miles) to protect the crossing sites at Mantes from medium artillery fire.

His 79th Division had that day engaged only scattered German groups in flight, had captured nineteen vehicles and a Panzer IV tank, and had received only sporadic machine gun fire from across the Seine.

Fortunately, a dam nearby offered a narrow footpath across it, and engineer assault boats and rafts could transport troops and light equipment.

While a torrential rain fell during the night of 19 August, men of the 313th Infantry walked across the dam in single file, each man touching the one ahead to keep from falling into the water.

The number of planes shot down in a day was a record for a World War II American antiaircraft artillery group.

On the east bank, the 79th Infantry Division not only extended and improved the bridgehead, repelled counterattacks, and interdicted highways, ferry routes, and barge traffic lanes, but also dramatically pointed out to the Germans their critical situation by capturing the Army Group B command post at la Roche-Guyon and sending the German headquarters troops fleeing eastward to Soissons.