MSea is a mine of information. Just to add a little to it.
The idea was to "sneak up" on the enemy, partly surface then fire at short range
and submerge quick.
It was never done in anger and probably wouldn't have worked The only thing
these boats were any good at was killing the crew one way or another.
Here's a couple of pics, just for interest. The first is a model in the science museum.
Haddock.
