WWII Pacific Theater ID Military Uniform

[bajafun]

Hi....My grandfather was a photographer during WWII, as part of the Seabees photo unit, and other "secret" details, in the Marianas, specifically mostly Tinian, also Saipan, Guam, and Yap. I came across this unusual photograph of military which seem to be dressed in unusual attire (to me). I thought at first they might be native Chamorro, but I can find no backup to that. Any help would be appreciated....or a reference to a useful site.

Thank you very kindly