here is the project B3 made by Bernardis in 1922: it is a preliminary project for a "large" submarine of about 2.700-3200 ton.
It was armed with two twin tuttets for 152/50, 4 torpedo tube in the hull (as usual) plus other 2 twin external torpedo tubes (adjustable).
No info about the turrets: probably sealed as the X1 but it is not evident the solution.
Anyhow the hull shows the wish for a fast unit...