First used by US forces that participated in the opperation Torch, to help gunners distinguish it from the French roundel.  Larger than standard roundel as the yellow ring was added to the outside of the existing roundels on the aircraft. It also helped to reduce incidents of Americans shooting down unfamiliar British aircraft, which could themselves be distinguished by a yellow outline on their fuselage roundels. It was later removed, except on aircraft that remained in the North African theater.