Here's the numbers you need to know for IFHE.  To see if you should use IFHE in the build of your current captain, just scroll down this list of the appropriate ship type and cross-reference the size of your ship's armament. -EDIT-  For those looking for the reasoning behind this summary: Destroyers Cruisers Battleship Secondaries There you go.  Your mileage will vary on select ships, but these should suffice for players who have reset their skills.