What was the purpose of the wolfpack during World War 2?

There were no surface ships in a U-boat wolf pack. (The submarines, like American subs, were called, "Boats".) The smallest wolf packs were 2 to 4 submarines, while the largest wolf packs could contain up to 20 submarines. The size of the wolf packs always depended on what their commander, Karl Doenitz wanted them to do.