I am trying to understand the basics of the conning tower.Please forgive my limited knowledge. To start with, am I right to understand that there is a hatch on top of the control room. This leads to the area inside the conning tower ( conning tower room). Above this little room is a hatch that leads to a small deck where people could stand.

Am I right that there are two hatches, one between conning tower "room" and control room and another leading from conning tower room to deck above ? If so , what is the purpose of having two hatches, when only one is needed at the top ?
Many thanks

Pras