A Nazi submarine is blown up during the Battle of the Atlantic, WWII

Local legend has it that a couple of Germans/Nazis landed on the island I live on during WWII and stayed in a remote cabin near where my house is now to observe American & Canadian shipping. That I believe. What I am skeptical about is the story that local fishermen here made improvised depth charges with barrels filled with some explosive and actually sank a Nazi submarine. The Battle of the Atlantic went on for the entire duration of WWII.