If you see the % marker as red is because the Crew is not trained for the specific Tank.

The effects of having a crew non specialized on the Tank they are handling affects in multiple ways:

• If the whole crew was driving a tank different from the one you transferred them on, the general performance of the tank will be poor; lets assume you are transferring your crew from a medium tank to a heavy tank, the driving skills of the driver will be lower and the capacity to detect enemy tanks by the commander will be lower as well, same applies to all the other roles of the crew members. (Imagine transferring the crew members of a private Jet into an Airbus 380!)

• There are other scenarios that can happen, for example, mixing crew members non-trained for the tank and others who are, in this case it will depend on the role; so for instance if the commander is trained for the tank you are using, but for instance the loader is not, you will spot enemies normally, but your re-loading performance will be poor. Take into account that the Tank Commander influences the whole crew, so a more specialized Commander will result on a better performing tank.

You can always re-train your crew from tank to tank, by right clicking your crew member, and selecting the Training tab of their profile, there you select to which tank you wish him to be re-trained; remember there are different types of training (50%-free, 75%-20000 igc,100% 200Gold) and as you might have noticed they also greatly influence the performance of the tank. Note however you can not transfer crew from Tank Destroyers into Light-Medium-Heavy Tanks, nor from SPG's to any type of tanks and vice-versa.

It is generally recommended to have your crew at least trained to 75%, if this is not possible try to train your commander and driver to 75%, they influence the general performance of the tank more than any other member.

If you want further info on crew members, their roles and effects on your tank read: Crew- World of Tanks

The tankopedia is a great place to browse through the available tanks.

SPGs

1. German
   • High damage/penetration
   • Long range
   • Small cone of fire
2. Russian
   • Lowest damage/penetration
   • Fastest reload
   • Shortest range
   • Largest cone of fire
   • Highest trajectory (can shoot targets behind cover easier)
3. American
   • Good damage
   • Great accuracy
   • Long range
   • High mobility
4. French
   • Good damage
   • Decent accuracy
   • Slowest reload
   • High Mobility
   • Long range