Final Answer:
The German submarines had to retreat after severe losses because of the Allied advancements in anti-submarine warfare tactics, technology, and the development of convoy systems.
Step-by-step explanation:
The German submarines, known as U-boats, faced significant setbacks due to the Allied advancements in anti-submarine warfare strategies and technologies during World War II. The Allies implemented convoy systems, where merchant ships traveled in groups escorted by warships, making it harder for U-boats to target and sink vessels. Additionally, advancements in sonar technology allowed the Allies to detect and track submarines more effectively.
Furthermore, the Allies improved their tactics for countering U-boat attacks, employing depth charges, improved aerial surveillance, and the use of long-range aircraft for patrolling and attacking submarines. These developments in anti-submarine warfare significantly increased the risks and losses for German U-boats, forcing them to retreat and adopt more defensive strategies, especially in the later stages of the war.