One thing no one mentioned is the DD crew AI. There are different settings on the skill level. Stock uses random levels. TMO has all the levels set to the highest. RSRDC sets them consistent with the period of the war, with some random differences. If you encounter a crew that is set to the highest level, then any historical accuracy doesn't count. That crew will be able to find you at night, while you are silent running below the thermal layer. Also, they will not let up until you are destroyed, they are out of cans, or have gotten too far from the convoy.
If you get a lowest level crew, then they could miss you during a clear day, while surfaced, and firing on them.
