Frequent aircraft activity made rapid diving especially important in the Mediterranean. A boat might need to submerge at a moment's notice during routine operations. Smaller submarines had an advantage in meeting that requirement. Getting below the surface was only part of the escape, because the hull also had to reach a depth where it could no longer be seen.
Notable Point · 7:57:34-7:58:24
Why Mediterranean submarines needed to dive quickly
Aircraft density and the need to disappear below visual detection favoured a small, quick-diving submarine.