Any port around the British Isles was a good hunting ground.
The British Isles are ISLANDS. Anywhere vessels enter those ISLANDS was "shipping traffic", or "shipping lanes"; those were always good hunting areas.
Principally the Imperial German Navy and the Royal Navy - both enormous forces at the time. Submarines and anti-submarine warfare were still in their infancy in WW1, but it was a German submarine that torpedoed the liner Lusitania off the coast of Ireland.
Uncivilized
Cowardly.
Germany practiced unrestricted submarine warfare.
"Guerre de Course"; Commerce Raiding.
Guerre de Course (Merchant Warfare).
submarine warfare
German submarine warfare
In almost all navies during WWII, submarines were called "boats"...not ships. In Germany, a sub was called an "under-sea-boat", with German enthusiasts preferring to use the German spelling/pronunciation of "boot" for boat. Bottom line: "U-Boat submarine warfare..." is simply submarine warfare (Sub Warfare is what most boys in America grew up calling it).
The connection between German submarine warfare & the battle of Stalingrad is a distant one............Ans 2 - The Battle of Stalingrad was fought between the Russian and German Armies and air forces. Submarine warfare was not a part of it.
The renewal of unrestricted German submarine warfare had devastating effects on shipping in 1917. In terms of tonnage, the Germans sank 540,000 tons in February 1917, 578,000 in March and 874,000 tons in April. Anti-submarine measures by the Allies, however, began to reduce this calamity.
unrestricted submarine warfare