As the planes are a long distance fore-and-aft from the hull's centre of buoyancy, they introduce a pitching moment.
If not carefully controlled, this could lead to a 'porpoising' motion whereby the planesman continually hunts for a stable combination of depth and pitch.
Earlier submarines (to World War II) used vertical folding planes perpendicular to their surface.
The depth control planes were mounted on the beam, so that they acted vertically, without the lever arm to introduce the usual pitch.
From the outset, diving planes were controlled remotely by telemotors, early servomechanisms operated electrically or by hydraulics.
For precise maintenance at periscope depth an additional shallow-depth manometer, a transparent vertical pipe, would be provided too.