2 last points on skills just in case you don't know.

The XP needed to gain a point increases ie it takes more xp to go from say 90 to 91 than it does from 50 to 51.

So those last few points always seem to take an age.

Then the XP needed doubles with successive skills

Assume you start with a 100% crew and are going for your first skill well that takes. 190,967 xp to go from 0 to 100%

You already have BIA probably as a zero skill meaning your next skill will count as your first.

Which is why the female crew and the other special crews are so valued those free skills.

Anyway

First skill 190,967 xp

Second 381,934 xp

Third 763,868 xp

And so on

Luckily a 2 skill crew is pretty darn good and a 3 skill one a little better but not so much as it completely outclasses the others.

Once you have the basic skill set for a tank the other skills are just fine tuning.