D-Day Normandy invasion in World War II

The transcript describes the initial landing of Allied troops on French soil during World War II. Despite facing significant challenges, including being confined to a narrow strip of beach and needing to take cover behind a seawall, the troops managed to create a small opening in the enemy's defenses. This breakthrough allowed for the eventual arrival of 4,000,000 men, leading to the successful establishment of the Normandy beachhead.

How many men were eventually to pour through the narrow opening?

What was established as a result of the Allied troops' efforts?