Did they have to calculate the change in the trim after taking on supplies?

Absolutely. The change needed to be calculated the night before going to sea. This was done by the officer on duty that last night in port. It was important enough that it was also checked by another officer. Then the duty officer was the diving officer for the trim dive the next day, for added motivation.

The calculation needs to include any crew members - and their gear - coming aboard or leaving the boat. An average number was used for the weight of a sailor and his gear. The calculation also included any added ammunition, food or supplies, and any changes to the number or types of torpedoes. The calculation also needed to include the decreased weight from adding fuel. Again, the fuel tanks had a compensating system that filled in water below the fuel as it was used so that the tanks did not need to be pressurized. A gallon of diesel fuel weighs about 1.5 pounds less than a gallon of sea water.