Trim tanks compensated as submarines burned fuel

How did submarines compensate for the different density of diesel and water as fuel was consumed?

They adjusted the trim tanks continuously so the changing liquid load did not make the submarine rise unexpectedly.

Trim tanks keep a submarine balanced as diesel is consumed and liquids of different density affect the boat. Crews adjust them as fuel use changes weight and balance, preventing an unintended rise toward the surface. Fuel management is therefore part of an ongoing trimming process rather than a fixed loading calculation.