brown bar

From the insignia of rank.

brown bar (plural brown bars)

1. (US, military, slang) A second lieutenant.
   • 1978, The MAC Flyer, page 25:

     Making a rather astute deduction from the fact that the brown bar in white fatigues was loaded down with a huge bottle of clear liquid and an assortment of tubes and needles, […]

   • 1991, Keith William Nolan, Operation Buffalo: USMC Fight for the DMZ, page 118:

     Afterward, Lindenmeyer made his way over to Lieutenant Turchan's radioman who, considering the brown-bar's greenness, almost appeared to be running the platoon.