FAC - Forward Air Controller...person who coordinated air support, usually flying in a small fixed wing aircraft like the Cessna 0-2 "Sky Master", with a split tail and "push-me-pull-me" props front and rear. He would verify our smoke or mark the enemy position with a rocket then call in the support aircraft.  This individual was essential when using non-rotary wing support, since we did not have the radios needed to talk directly to the support aircraft.

Don't know where I got this picture from...if it is yours, my apologies. Let me know.