First aid tent
The First Aid Tent is one of the War Machines, like the Ballista, the Ammo Cart, and the Catapult. After all units have been cycled through once in a combat round, it heals up to 25 of the damage done to one stack. Having the Secondary Skill First Aid will greatly increase its performance by healing more damage and allowing you to choose the target to be healed.
It can be bought in a Blacksmith in a Rampart, Fortress, or Necropolis, or at a War Machine Factory on the Adventure map. Heroes specializing in First Aid usually come with a First Aid Tent.