Why was it important for the Allies to breach Hitler’s Atlantic wall

Probably the most important thing was the ability to coordinate an amphibious attack on the beaches and to bypass the German defenses.

Explanation:

Atlantic Wall was created by the Germans so they prevent the Allies to easily breach their defense system. It was strengthen throughout the war and the Allies had different opinions on how they would attack the enemy. When the operation D-day became operational they realized that they need also to attack Germans from the back, as it was impossible to attack them only by sea.

mass production/ assembly line production

this isn't a question and if you're going to list things be kind and use commas.