no idea about the mission, but if it was for arma3, very likely it was the Unsung vietnam war mod, which is the "go to" vietnam mod for arma3 - https://steamcommunity.com/sharedfiles/filedetails/?id=943001311

SimHQ Arma3 sessions, weekly semi-serious co-op action for all ages and skills! check the forum sticky for more info!

http://simhq.com/forum/ubbthreads.php/topics/3732626/SimHQ_Arma3_Sessions,_who,_wha#Post3732626

All spelling errors are included free of charge and courtesy of a broken spell checker!