Good news
Using Notepad++ I have searched the data folder for the string "WP_FLAK_GUN", and I found instances of it in the following files:
\Scripts\AI\Crew\Crew_Idle_Actions_QR2.aix
\Submarine\NSS_Uboat7*\Submarine Parts\Conning_7*.GR2 (this was expected)
\Submarine\NSS_Uboat7c41\Submarine Parts\Conning_7c41_*.waypoints.GR2 (this was expected too, but I still don't get why only VIIc41's conning towers have their crew waypoints duplicated in an external GR2 file; makes me wonder whether the duplicated bones are actually used or not)
\Submarine\NSS_Uboat7*\waypoint_edges.txt
\Submarine\NSS_Uboat7*\waypoint_info.txt
Now we need to study those files, but I feel we are a step closer to the solution of the puzzle
