Groß Admiral Karl Dönitz for loosing the most men on one Battlefield then any other in any other Battlefield during WW II. Worldwide.
I'm not sure how you came to this conclusion. Donitz was only the 'Grand Admiral' from January 1943 on wards. The German losses were 30, 000 dead in the battle of the Atlantic for the entire war. Perhaps add another 10, 000 to cover the losses of other surface raiders and we have about 40, 000 dead over 6 years covering oceans.
Compare that 6 year battle with a few other short battles.
Battle of the Bulge, German casualties 100, 000
Battle of Stalingrad, German casualties 800, 000
But to be fair, if you lump all of the atlantic and 6 years into one battle, then compare that with the battle against Russia where 40, 000 died in a day a few times. The battle at Kursk produced 170, 000 casualties and that was over in a day or two.
Donitz got a bum rap!