Well easyest way would be to use your ESM mast and/or Periscope. Otherwise you will want to determin the blade count of the contact's screw(s) using DEMON and compare that to the potentional NB classifications numbers of blade in the USNI ingame browser. If you still have more than one possable class then try and find the ships speed and go to DEMON and imput the TPK of the possable classes. If that dosn't get you the class well... take a guess.
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