[Crannogman]

I left Pearl in early '42 with a new Gato and RSRD. I found the hunting incredibly austere, to the point where I snuck into a harbor in Formosa and sank 5 ships. Then I started getting contacts reports suggesting a shipping route, and started down it. Still nothing on sonar, then a medium freigher loomed out of the fog dead ahead. A few days later in the Bungo Duido, I was able to confirm that I my sonar only worked when I was submerged.
I though RSRD only changed campaign stuff, not AI and sensors etc. Anyone have any idea if it's RSRD, or maybe the Gato?