The success of the amphibious landings depended on the establishment of a secure lodgment from which to expand the beachhead to allow the build up of a well-supplied force capable of breaking out. The amphibious forces were especially vulnerable to strong enemy counterattacks before the build up of sufficient forces in the beachhead could be accomplished. To slow or eliminate the enemy's ability to organize and launch counterattacks during this critical period, airborne operations were used to seize key objectives, such as bridges, road crossings, and terrain features, particularly on the eastern and western flanks of the landing areas. The airborne landings some distance behind the beaches were also intended to ease the egress of the amphibious forces off the beaches, and in some cases to neutralize German coastal defence batteries and more quickly expand the area of the beachhead. The U.S. 82nd and 101st Airborne Divisions were assigned to objectives west of Utah Beach. The British 6th Airborne Division was assigned to similar objectives on the eastern flank. 530 Free French paratroopers from the British Special Air Service Brigade, were assigned to objectives in Brittany from 5 June to August.