Folks,

Modern submarine design are designed exclusively for underwater travel so they have the most hydronamic shape for underwater travel. A WW2 sub had to travel on the surface for most of its patrol so it had to have a hull form that was compatible with surface travel. If you see pictures of modern submarines running on the surface you can see a large wash running up over the deck and a wide very prominant wake behind the sub. These features show that the sub's hull form is very inefficient on the surface and is an indication of the huge 'drag' created by the hull on the surface. Underwater is a differnet matter, Albacore could make 33 knots with 15000 shp but could cruise underwater at 6 knots with just 136 shp. Comparable 'traditional' hull designs (i.e similar displacement) could not evenapproach 33 knots underwater,no matter what horsepower they had installed and needed 300 shp+ to make 6 knots underwater. The type XXI became dynamically unstable above about 14 knots so even if she could have gone faster,which would have been very difficult given her hull form,she would have been so unstable as to be dangerous.

Rgrds

Sniper.