Answers of your questions are in DW manual and Weapon guide manual for RA.
This second manual is MANDATORY for RA
USET-80 is wireless torpedo - it means you cannot change searching depth after launch.
In RA some of wire-guided torpedoas has abilities for changing depth to under/above layer - all informations are in "Weapon guide" manual.
P.S. if you don't like to read manuals, you should stay with vanilla DW
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