The shoulder rope of aid-de-camps to general officers stems from the practice of both and French and English officers serving in th functions of aides wearing a rope with a pencil tied to the end of it to have it handy for transcribing orders from thier General. That transferred over to the Contitental Army.
The Marines (2/6th and a regiment from the 5th) were awarded the French Fourrage after WWI and contiue to wear it as tradition.
Not sure why the Infantry wears the blue rope. Didn't cover that at Knox or NJROTC. lol
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