It’s not really “weird” - the design allowed the crew to leave the submersible unassisted when it was on the surface, which would be optimal for safety.
The tunnel provided a route from the crew sphere to the top of the float. During the dive it was used as a ballast tank and filled with water. Compressed air was carried to blow the water out at the end of the dive.
The original design had an open conning tower, but it was found that waves could break over it and potentially flood the diving bell if its hatch was open - hence a door was fitted. The tower was supposed to be pressure equalised, so why the door’s plexiglass cracked is a puzzle - perhaps a thin sheet will crack when exposed to a very large static pressure?
The tunnel provided a route from the crew sphere to the top of the float. During the dive it was used as a ballast tank and filled with water. Compressed air was carried to blow the water out at the end of the dive.
The original design had an open conning tower, but it was found that waves could break over it and potentially flood the diving bell if its hatch was open - hence a door was fitted. The tower was supposed to be pressure equalised, so why the door’s plexiglass cracked is a puzzle - perhaps a thin sheet will crack when exposed to a very large static pressure?