Herr Kaleu browsergame
 

Looks like SHO may have some competition in the sub sim browsergame arena, German developer Mr Mot has is developing "Herr Kaleu", though perhaps not as nice graphically as SHO (reminds me of the EGA Sub Battle Simulator) it does seem more in-depth in terms of available technologies & options. Check it out here (scroll down on the page for blog screenshots)