Operation OVERLORD: The D-Day Invasion On June 6, 1944, 9th Air Force units, along with aircraft from the USAAF 8th Air Force and the British Royal Air Force, hammered enemy positions. Thanks to the pre-invasion effort, there were virtually no Luftwaffe aircraft in action on D-Day. With most of the bridges leading into Normandy destroyed, the German army found it very difficult to bring in reinforcements, and their relief forces remained under almost constant air attack as they tried to move forward. In the weeks following D-Day, the Allies tenuously held onto the beachhead and worked feverishly to bring in troops and supplies faster than the enemy. Ninth Air Force interdiction of enemy troops, tanks and supplies proved critical in tipping the balance in the Allies' favor. Click here to return to the Tactical Ground Attack in Western Europe Overview.