Every weapon, regardless of gun or torpedo tube, has an "ammo bunker" entry in the .eqp file.
So if you leave that blank, you basically have a non reloadable torpedo tube
Every time one of those italian convoys passed me in the med in SH3 GWX, I wished I had a british sub instead of a VII
As I said, I have no idea about british subs other than basic technical data and the usual "greatest heroics" stuff.
I sofar have not found a serious operation british sub history, like some kind of british equivalent to "silent victory"