The American airborne landings in Normandy by IX Troop Carrier Command were the first United States combat operations of Operation Neptune, (the assault operation for Overlord). 13,100 paratroopers of the U.S. 82nd Airborne and 101st Airborne Divisions made night parachute drops early on D-Day, followed by nearly 4,000 glider troops flown in by day in six missions. The divisions were assigned to support the U.S. VII Corps in capturing Cherbourg (to provide the Allies with a port of supply) by blocking approaches threatening the amphibious landing at Utah Beach, capturing exits off the beaches, and to establishing crossings over the Douve River to assist the merging the two American beachheads. The assault did not succeed in blocking the approaches to Utah for three days. Numerous factors played a part, most of which dealt with excessive scattering of the drops. Despite this, German forces were unable to exploit the chaos. Many German units made a tenacious defense of their strongpoints, but all were systematically defeated within the week. A follow-up operation was scheduled in which one wing of IX TCC would deliver the British 1st Airborne Division to Évrecy on June 14 to support a breakout attempt by British armored forces (Operation Wild Oats) but was so perilous that airborne and troop carrier commanders agreed to it only reluctantly. Crews were being briefed on June 13 when a strong German counterattack at Villers Bocage forced cancellation of the drop.