Although many USAAF/USAAC units did use the various US insignia with a red outline, units in the Pacific specifically avoided using ANYTHING that remotely resembled a red circle, for obvious reasons. The red was also removed from roundels, and the red outline was either never applied or was removed from both the round insignia with the white star on a blue circle and the star/bar insignia. I was reading about this within the last couple of weeks, and saw it mentioned in several places and sources.