First allied bridgehead across the Seine

Seine River Crossing at Mantes-Gassicourt
Part of Operation Overlord, Battle of Normandy
Date 18–20 August 1944 Location Present Day Mantes-la-Jolie, France 49°0′31″N 1°41′12″E / 49.00861°N 1.68667°E / 49.00861; 1.68667Coordinates: 49°0′31″N 1°41′12″E / 49.00861°N 1.68667°E / 49.00861; 1.68667 Result Allied victory
Belligerents
United States	Germany
Commanders and leaders
George Patton Ira T. Wyche Joseph Bacon Fraser
Casualties and losses
None	43 aircraft shot down 1 Panzer IV tank and 19 vehicles captured

General George Patton's Third Army's Seine River Crossing at Mantes-Gassicourt was the first allied bridgehead across the Seine River in the aftermath of Operation Overlord, which allowed the Allies to engage in the Liberation of Paris. During the two days of the bridge crossing, American anti-aircraft artillery shot down almost fifty German planes.

After the successful allied invasion of Normandy in June 1944, The United States Third Army was formed in France to assist in the breakout from Normandy, code named Operation Cobra. 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 Mayenne River, clear the area west of the Mayenne River as far south as the Loire, and protect the 12th Army Group south flank with minimum forces. Since the VIII Corps was driving southwest toward Rennes and the XV Corps was about to move southeast toward Mayenne, Patton oriented the XX Corps south toward Nantes and Angers. As the main American effort veered eastward in accordance with the modified OVERLORD plan and the XV Corps drove toward Laval and Le Mans, Patton ordered the XX Corps to cross the Mayenne River in a parallel drive to protect the XV Corps south flank.

The Third Army's XV Corp drove from Meyenne South to Le Mans and then North to Argentan by 12 August 1944 where the Battle of the Falaise Pocket was developing against the German Seventh Army . The next day, the 5th U.S. Armored Division of XV U.S. Corps, advanced 35 mi (56 km) and reached positions overlooking Argentan. On 13 August, Bradley over-ruled orders by Patton, for a further push northwards towards Falaise, by the 5th U.S. Armored Division. Bradley ordered the XV U.S. Corps to "concentrate for operations in another direction". The U.S. troops near Argentan were ordered to withdraw, which ended the pincer movement by XV U.S. Corps. Patton objected but complied, which left an exit for the German forces in the Falaise Pocket.

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