Keep in mind that there are five levels of submarine warfare.
1. Very few ships get through. Think Russia in 1942.
2. Few ships get through and the Allies are not able to seriously bomb German cities and interfere with industrial production or supply a French invasion. Think Malta in 1941.
3. More ships get through and the Allies are only able to annoy German cities and perhaps invade North Africa. Think North Africa in 1942.
4. Most ships get through and the Allies win the war. That was 1943.
5. Almost all ships get through but you at least make them delays ships to form convoys, and build escorts and use up multiengine aircraft on antisubmarine patrols instead of bombing raids. That was 1944.
1. Very few ships get through. Think Russia in 1942.
2. Few ships get through and the Allies are not able to seriously bomb German cities and interfere with industrial production or supply a French invasion. Think Malta in 1941.
3. More ships get through and the Allies are only able to annoy German cities and perhaps invade North Africa. Think North Africa in 1942.
4. Most ships get through and the Allies win the war. That was 1943.
5. Almost all ships get through but you at least make them delays ships to form convoys, and build escorts and use up multiengine aircraft on antisubmarine patrols instead of bombing raids. That was 1944.