Short answers, pulled from the story.
The Battle of the Atlantic lasted from 1939 to the defeat of Nazi Germany in 1945. It was the longest continuous military campaign in World War II, stretching over five years before the German surrender in May 1945.
The campaign pitted U-boats and other warships of the German navy and aircraft of the air force against the Royal Navy, Royal Canadian Navy, United States Navy, and Allied merchant shipping. The Germans were joined by submarines of the Italian royal navy after Germany's Axis ally Italy entered the war on the 10th of June 1940.
Ships and aircraft of the United States began aiding the campaign on the 13th of September 1941. The United States officially entered the war in December 1941, leading to the organization of a Mid-Ocean Escort Force of British, Canadian, and American destroyers and corvettes.
The outcome of the battle was a strategic victory for the Allies, as the German tonnage war failed. The Allies lost 3,500 merchant ships and 175 warships in the Atlantic for the loss of 783 U-boats and 47 German surface warships.
The United Kingdom required more than a million tons of imported material per week to survive and fight, making the nation highly dependent on imported goods. Without these supplies, the British war effort would collapse, and the nation would be forced to surrender.