How torpedo-bulge compartments changed in service

Were torpedo bulges empty, subdivided, or deliberately filled?

They were subdivided, and their compartments could be void, flooded, or used for storage according to the ship and period.

Torpedo bulges were not always permanently empty chambers. Early schemes often emphasized void spaces, but later practice could flood compartments or use available volume for storage. Subdivision limited the consequences of damage and gave designers operational choices. The correct description depends on the vessel and the date because the contents also affected buoyancy.