Feldunterarzt
According to the rank hierarchy , it was comparable to Sergeant First Class ( de: "Oberfeldwebel" ) or Chief Petty Officer ( de: "Oberbootsmann" ) NATO-Rangcode OR-7 
<triplet> Oberfeldwebel <subj> Oberbootsmann <obj> said to be the same as <triplet> Oberbootsmann <subj> Oberfeldwebel <obj> said to be the same as