Why Did America Develop a Submarine Fleet in 1942

Why did America develop a submarine fleet in 1942?

A) to prepare for an invasion of the Italian coast that would fulfill Stalin's demand of a second front
B) to stop Japanese shipments of food and oil because Japan was dependent on imports
C) to guard British merchant ships since Britain did not participate in the Lend-Lease policy
D) to protect German refugees, such as those on the Wilhelm Gustlo
E) to aid British troops in North Africa, helping to preserve the British empire