Ahh - my cute but sadly very weak Light Aircrat Carrier USS Long Island ...

... I don't wanna to be pedantic, but the medic told me to so...

This image is inaccurate! Long Island has only 2 skills (1 if not retrofit) - one is a Red (Attack) skill and the other is a Yellow (Support) one - this means - using BLUE skill books as depicted in the picture will grant reduced skill exp gains - a mindful player should only provide her with red and yellow skill books :<

But the red skill book always depleted if you keep on training all your ships, so you often end up using them.

Blue books are always too-much. I use them to gain red or yellow skill EXPs, when not at armament tension (usually during events).