Final answer:
The Atlantic Squadron was reorganized into the Atlantic Fleet in early 1941 to increase the US naval presence and protect Allied convoys against increasing U-boat attacks in the Battle of the Atlantic.
Step-by-step explanation:
The Atlantic Squadron was reorganized into the Atlantic Fleet in early 1941 largely as a response to the increasing hostilities and hazards posed by German U-boats in the Atlantic Ocean during World War II. Prior to the United States formally entering the war, President Franklin D. Roosevelt had expanded the US naval patrol and escort service to safeguard shipping bound for England. The confrontations between German U-boats and US naval forces were escalating, evidenced by the torpedoing of the U.S.S. Reuben James, leading to significant casualties. The reorganization into the Atlantic Fleet bolstered the US naval presence in the Atlantic, contributing to the protection of Allied convoys and maintaining open supply lines, critical for the Lend-Lease program that supported Britain and the Soviet Union. The surge in Allied capability to produce ships and advancements in anti-submarine technology like sonar were pivotal in winning the Battle of the Atlantic, which was crucial for the success of Allied operations including the invasion of North Africa and the eventual D-Day landings.