Vitality is a crew skill available for all crew positions in ground and air vehicles.
This skill reduces the likelihood of a crew member receiving a mortal wound. For the novice pilot the second .303 bullet hit or comparable shrapnel impact is usually fatal; while a pilot with the vitality maxed out can, with a measure of luck, survive one hit from a .50 (12.7mm) M2 Browning machine gun. Against direct hits from cannons, however, there is little this crew skill can change.
While the skill is useless against direct tank shells that penetrate your armor, the skill is more useful against armor spalling and when your crew is exposed to enemy machine gun. When the enemy penetrates your armor (or hit it with a powerful enough HE round), dangerous shrapnel flies around in the tank compartments, which the skill can help mitigate the damage to the crew. Exposed crew members with this skill can help reduce the likeliness of being instantly killed by a tank's machine guns.