There's a port in a bay on the Northern end of the arc for the "Sink 50,000 Tons in English Costal Waters " mission.
After running on the foggy surface at all ahead full right by four destroyers on screen duty, I was hoping to find just a tanker or two in port. Instead, I found 12 parked destroyers. I proceeded to sink 9 of them.
It wasn't until the 8th went down that the harbor screen force even responded.
By the time the 9th went down I had 4 destroyers on the surface, and I was at periscope depth with only a few meters of clearance from the ocean floor. Their pings were continually ringing off my hull now. - yes if death by pinging was possible, I was indeed "dead".
After evading a single DC salvo that got "in the ballpark", I went to silent running, dead slow, and slowly crawled past the lip of a deeper channel, and then ran under the thermal layer at 50m - and got away with 1% hull damage.
So 9 destroyers later, having completely crippled the main convoy escort and patrol squadron for all of Northeast England, I would indeed hope this has some effect on the ground war... but I know it doesn't.