I read a book about an officer that was parachuted into Burma in WWII to attempt to rescue downed aircrew. They would fly out to what they thought was the area where a rescue was needed, he would parachute out and report back to the airplane via a BC-611 hand held radio. If he had located the aircrew they would drop supplies and perhaps even a medical team and then walk or boat out of the jungle. Sometimes they were able to get to a point where a 4X4 could reach them on the ground. Mostly the terrain did not allow them to be flown out but they eventually did make use of the first helicopters. He was the first to practice "pararescue."