A quick google search of the site for anything related to 2.6 yielded this thread
http://www.subsim.com/radioroom/showthread.php?t=118005
Seems that what we've all come to know as NSM (Natural Sinking Mechanics) was originally titled RSP (Realistic Sinking Physics).
See about 8 down on the first page
http://www.google.com/cse?q=2.6&cx=0...www.subsim.com
Needless to say, everything RR said is right