Indicator for sunked ship...
 

After you sank a ship, you will see on the map (F5) an indicator in that point.
What do these different colors mean: red, blue, green and gray for the indicator? What does it mean when the indicator is missing from the map?

Red=enemy
Blue=Axis
Green=neutral
Gray=unidentified

If you torpedo a ship and it doesn't sink-no credit\no icon. Usually in bad weather or you are forced away , do I get no icon normally.

They are identified but sometimes i sunk a ship i does not appear any indicator! One of my bugs!

There are two possible reasons. One is that you made changes to your U-boat before going out on patrol in your first career patrol. This is a known game bug. When in a career, do not make any changes to your boat configuration before going out on your first patrol. After that you may make changes to your boat.

The second reason is if you sink ships in shallow water. You may not get credit for a ship that settles to the seafloor in shallow water. This sometimes happens when you raid an enemy harbour. The upper part of the ship sticks out of the water and though the keel is bottomed, the game may not recognize this as a sunken ship and give your credit.