http://wiki.worldoftanks.com/Crew#Skills
This perk increases the training level of each crew member's Role/Major Qualification by 5%. It also improves the Repair, Firefighting, and Camouflage skills by 5%. As of 8.2 it also improves commander's Mentor skill. It does not affect other role-specific skills, nor any perks (in-game description is incorrect).
There is no benefit whatsoever unless all of the crew have this trained to 100%. The perk stays in effect if a crew member is knocked out during battle. The perk is cumulative with Improved Ventilation and skill boosting consumables.
