For many veterans of the Vietnam war, it is a bitter memory.
For army helicopter gunner John Metzler out of Idah he didn't have it easy.
But there was one thing that got him through the deadly conflict - a thank you note from a stranger written by a young girl Donna Caye.
John still remembers the day he received the letter, it was Christmas day in 1970.
And this is what it said: "Dear serviceman, I want to give my sincere thanks for going over to war to fight for us. The class hopes you will be to come home."
For decades, John has tried to track the Donna Caye - the mystery writer.
He wasn't sure if he would ever get to meet her but just this month Donna Caye discovered John had been searching for her.
So she decided to write him another thank you note. This time it travelled Florida to Idaho and delivered by Donna Caye by hand.
Watch the video.