MEDEVAC is normally performed by the US Army although every branch of the armed services have procedures for evacuating casualties. MEDEVAC is different from casualty evacuation in that MEDEVAC units don't knowingly go into hot zones because they are not combatants. MEDEVAC is the transportation of the wounded warrior to a hospital rather than a casualty collection point or an aid station. I am using Army terms here. Some of you marine corps military ring customers may use different terminology. The Air Force uses its pararescue to locate and evacuate downed pilots which is different from MEDEVAC.

In the event a soldier has to be evacuated from a combat zone a casualty evacuation vehicle is used. This will be a vehicle organic to the soldiers unit which is armored for protection or it may be a lightly armed helocopter. Once the casualty is moved to a safe area he can be MEDEVAC'ed  to hospital where he can be  treated for more serious injuries.

During peacetime all custom US Army military ring customers are drilled on MEDEVAC procedures and call signs. if a soldier is wounded or injured during training the training is halted and the MEDEVAC will come directly to the units location. If his injury is not serious or life threatning he will be evacuated to the units aid station to be treated and released.