I agree w/ almost everything Frankster said. Except, from what I gathered from the original comic, Duke was brought in to kick booty in GI Joe ranks. His rank really had nothing do w/ the overall scheme. Hawk looked for the best man he could and he found Duke. 1st sgt, Lt, whatever... Duke had what it took. That's how I see the comic Duke.

Cartoon Duke... Uhmmmmmm...