Hi CL
There is quite a big band of RC sub modellers some of which are scratch built here
www.scale-models.co.uk. See also the U-Boat ''Mylo'' Hall built, this thing absolutly dwarfs the 1:72 Revell U-Boat. Click here
If the 1/72 U-boat is too big for you...
Hope this is of some help,
Sav.