[GunMaster357]

Sonar detection in WWII was in its infancy as no country had ever imagined submarines deployed on the scale used by Germany. So, part of the game was to play dead up to push oil, debris and even bodies through a lock.

Never forget that this era was the first time submarines were used as an effective weapon integrated as such in the navy at least in Germany. In other countries, they were considered something of a special weapon to be use at specific places and moments, or even worse, as toys.

Therefore, it's only logical that designers didn't think of every contengency.

Back to the problem of space.

A submarine, even today, has a very delicate equation to solve: flotability. If you put too many things in it, once you dive, you wont be able to resurface again.

For example, a bathyscaphe (very deep water exploration vessel - down to 30000 feet) do not use ballasts to dive but an enormous steel weight that is left on the ocean floor once they want to get back to the surface.