I've been reading u-boat POW interrogation reports on u-boat archive and found S-Gerät mentioned twice. A quotation:
(ii) "S-Gerät" (Detector Gear)
"U 574" was stated to have been fitted with a form of "S-Gerät," which could be inclined 80 up and down and also sideways. This S-Gerät was stated to have a range of 400 metres, and to be used only for detecting nets or minefields. Prisoners stated that a visual indicator (Mattscheibe) was employed; it was not often used for fear of betraying the U-Boat's position.
http://www.uboatarchive.net/U-574INT.htm
Another prisoner report stated the same purpose and a range of 500 meters. It is only a prisoner report, but can somebody confirm this? Was the S-Gerät so limited? If so, the game version of the S-Gerät is way über.