Every time you unlock a new tank, you're prompted to recruit its Crew. Similar to Tank XP, Crews accumulate Crew XP for every battle in which they participate.
All Crews start with a base mastery level of 50% with "Rapid Courses." It will take many battles to advance your Crew to 100%, but once fully trained, a new level of options become available.
Mastery level determines the effectiveness of a Crew
You can also advance Crews training via currency; send them to "Regimental School" for 75% mastery (for some Silver) or to the "Tank Academy" for 100% mastery (for Gold). The higher the mastery level, the more effective the Crew in battle.
One of the easiest ways to train a Crew is with either Premium vehicles or Elite status vehicles. Premium vehicles cost Gold. Regular vehicles become Elite when you research all of their packages and the vehicle that follows.
Crew Benefits from Elite Vehicles
"Accelerated Crew Training" available when vehicle becomes "Elite"
Crew Benefits from Premium Vehicles
Transfer Crews from a regular vehicle to a Premium vehicle of the same nation for additional training in battle
"Accelerated Crew Training" available from the outset
Swapping Crews between regular vehicles costs Gold or Silver, but you avoid the cost when assigning to another Premium vehicle of the same nation. It's the number one reason why Premium vehicles are best for training Crews.
There are also special Operations (Ops) and in-game modifiers that can help accelerate Crew training.
Boost Ops and Crew XP Multipliers
Crew Boost Ops: Earned via select Ops or bought in the Store. They increase the Crew XP earned after individual battles
Crew XP Multipliers: Available via Ops, special game events or as part of Store bundles
After a Crew reaches 100% proficiency, it's time to consider Skills and Perks, which can drastically change the way you play.
Skills and Perks
Do not neglect your Skills and Perks
You have many options!
Skills and Perks give Crews valuable boosts in battlefield performance.
Just like training, a Skill or Perk begins at 0% proficiency and increases the more the Crew is used. Nevertheless, Skills and Perks operate differently...
Skills vs. Perks
When deciding what to teach a Crew, it's important to consider if you'll benefit from the immediate effects of a Skill, or if you can stomach waiting for the effects of a Perk to kick in.
Skill: Activates immediately, and its effectiveness will increase as it progresses to 100%.
Perk: Doesn't activate until it reaches 100%.
"Sixth Sense" is a go-to Perk for many -- it says when you've been detected by an enemy. This is crucial, yet it won't work until it's at 100%.
"Repairs," as its name suggests, is a Skill which accelerates the speed of repairing damaged modules. Though you also build this one up to 100%, it has some effect as soon as it's active.
The decision is yours... but if a chosen Skill or Perk isn't working out for you, you can drop it and replace it with another. This action costs 10 Gold.
Crews are reassigned to another vehicle of the same nation regardless of vehicle class. However, reassigning a Crew requires retraining them, so it's back to the familiar "Regimental School" or "Tank Academy."
Reassigning a Crew to a new vehicle requires retraining
You might become attached to your early Crews -- your first and most battle-hardened. They'll have a high mastery level and maybe a few Skills and Perks available to them.
It may have been fun battling with the Hetzer, but that new StuG III G will face tougher competition, and merits a battle-hardened Crew. The only way to give your StuG the experienced Crew it deserves is by reassignment!
Every Commander in your Garage will receive a military-based rank associated with their respective country. As your Crew gains more XP, they'll be promoted to more prestigious ranks. These ranks are just indicators of how battle-hardened your Crew is; they don't offer any in-game effects.