targets difficult to see. Concerned about inflicting casualties on their own troops, many bombers delayed their attacks too long and failed to hit the beach defences. The Germans had 570 aircraft stationed in Normandy and the Low Countries on D-Day, and another 964 in Germany. Minesweepers began clearing channels for the invasion fleet shortly after midnight and finished just after dawn without encountering the enemy. The Western Task Force included the battleships , , and , plus eight cruisers, twenty-eight destroyers, and one monitor. The Eastern Task Force included the battleships and and the monitor , twelve cruisers, and thirty-seven destroyers. Naval bombardment of areas behind the beach commenced at 05:45, while it was still dark, with the gunners switching to pre-assigned targets on the beach as soon as it was light enough to see, at 05:50. Since troops were scheduled to land at Utah and Omaha starting at 06:30 (an hour earlier than the British beaches), these areas received only about 40 minutes of naval bombardment before the assault troops began to land on the shore. Airborne operations The success of the amphibious landings depended on the establishment of a secure lodgement 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 counter-attacks before the arrival of sufficient forces in the beachhead could be accomplished. To slow or eliminate the enemy's ability to organise and launch counter-attacks 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 neutralise 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, where they hoped to capture and control the few narrow causeways through terrain that had been intentionally flooded by the Germans. Reports from Allied intelligence in mid-May of the arrival of the German 91st Infantry Division meant the intended drop zones had to be shifted eastward and to the south. The British 6th Airborne Division, on the eastern flank, was assigned to capture intact the bridges over the