The First Aid Kit is usable item. It is used to heal injured commandos completely. Any commando can carry and use this item. In the gameplay, the Driver is the primary "team medic". When the Driver is not available in the mission, the Sniper takes place. If the two are not available, the Spy becomes the medic.
The First Aid Kit can be applied to all commandos. But it cannot be used to other characters like the Gurkhas, Allied Soldiers and many more. The First Aid Kit is the only healing item that can heal a commando completely, even when it is dying. When the difficulty is "hard", you can't use the First Aid Kit to revive severely injured or dying commandos. This is due to the fact that they are "dead".
To use it, click on the icon and the cursor will become a syringe filled with red liquid. Then click on the target commando and the commando will be healed completely. You can also use the Hotkey C.
The First Aid Kit has only 10 shots, so the player must use it wisely.
In Destination Berlin, First Aid Kits are now "auto-used" when taking damage however on the Original difficulty in the remaster/only difficulty in the original game, this mechanic is broken and will cause an entire stack of First Aid Kits to be used automatically yet only restore the health of a single kit.
This nasty bug makes a hard game much harder but it can be avoided by keeping first aid kits on a Commando out of danger and having him use it on anyone injured or putting the First Aid Kits inside a container and removing a single kit (by holding Shift and Clicking) and closing the inventory so only that one single kit is auto-used.