What were some of the obstacles and hardships that American soldiers and commanders had to overcome on D-day?

The Allied Invasion of Normandy paved the way for the overdue opening of the Western Front against German forces. The operation was mired in overwhelming logistical, tactical and strategic uncertainties. The first was maintaining secrecy to ensure a rapid and surprise landing. Most of the Normandy beaches were well fortified and prepared for such landings including obstacles of tank and landing traps, turret and machine gun nests, bunker-tunnel-trench networks and armor divisions in the vicinity. Commanders had to devise a naval bombardment strategy to "soften" these obstacles. Daring drops of airborne special forces were needed to disable defenses behind enemy lines. Army Ranger units had to scale cliffs while under rifle and grenade attacks. Regardless of these odds Operation Overlord as it came to be known was a success and safe beachhead was established soon after.