Hi,

yes, you are right - there are two hatches.

The hatch between the control room and conning tower is required for safety reasons.
The conning tower - as the structure protruding above the hull, is exposed to damages from ramming (when boat is operating at periscope depth or near the surface). In such case, if conning tower structure would be damaged, there has to be way to isolate it from the rest of the boat. When the conning tower is flooded, you can shut the hatch between the conning tower and control room.

--
Regards
Maciek


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