I'd have to say "Letters from Home" by John Michael Montgomery. I think most sons want their father's to be proud of them, and I have a soft spot for the military... If you watch the video, it makes it that much worse (I don't think I've ever made it through without my eyes watering)
Here's a link to the video
http://music.aol.com/video/john-michael-montgomery-letters-from/john-michael-montgomery/1133313My Dearest Son, it is almost June,
I hope this letter catches up to you, and finds you well
Its been dry but they’re calling for rain,
And everything's the same ol’ same in Johnsonville
Your stubborn 'ol Daddy ain’t said too much,
But I’m sure you know he sends his love,
And she goes on,
In a letter from home
I hold it up and show my buddies,
Like we ain’t scared and our boots ain’t muddy, and they all laugh,
Like there’s something funny bout’ the way I talk,
When I say: "Mama sends her best y’all"
I fold it up and put it in my shirt,
Pick up my gun and get back to work
And it keeps me driving me on,
Waiting on letters from home
My Dearest Love, its almost dawn
I’ve been lying here all night long wondering where you might be
I saw your Mama and I showed her the ring
Man on the television said something so I couldn’t sleep
But I’ll be all right, I’m just missing you
And this is me kissing you
XX’s and OO’s,
In a letter from home
I hold it up and show my buddies,
Like we ain’t scared and our boots ain’t muddy, and they all laugh,
'Cause she calls me "Honey", but they take it hard,
'Cause I don’t read the good parts
I fold it up and put it in my shirt,
Pick up my gun and get back to work
And it keeps me driving me on,
Waiting on letters from home
Dear Son, I know I ain’t written,
But sittin' here tonight, alone in the kitchen, it occurs to me,
I might not have said, so I’ll say it now
Son, you make me proud
I hold it up and show my buddies,
Like we ain’t scared and our boots ain’t muddy, but no one laughs,
'Cause there ain’t nothing funny when a soldier cries
An' I just wipe me eyes
I fold it up and put it in my shirt,
Pick up my gun and get back to work
And it keeps me driving me on,
Waiting on letters from home