It's probably odd for me to give feedback now, but just wanted to plug and say that NYGM has done its work for me. On my IXD2 career, despite having spent over 500 days at sea between late 1942 and 1945, I had managed to sink a meagre 23 ships for 120,000t - that's despite the boat's big torpedo load.
For me, the "Tonnage War" has been almost won, I believe.