Just a note on army callsigns-Helo.l  Darkhorse  was the callsign of D Troop, 1st Squadron, 4th US Cavalry of the First Infantry Division from 1965 to March 1970.  When the Big Red One went home in Mar 70, the troop changed names to C Troop 16th Cav and became an independent air cav troop under the 164th Combat Aviation Group (CAG) based first at Soc Trang and later at Can Tho till the end of hostilities.  A/C were UH-1B/C/D/H, and AH-1G and OH-6A.
Hugh Mills
LTC, USA ret
Darkhorse 16, 69&72
Charliehorse 38, 71