In the NATO phonetic alphabet, the phonetic spelling of the letter V is Victor while the phonetic spelling of the letter C is Charlie. During the Vietnam War, the Vietnamese Communist guerillas we’re referred to as Viet Cong. This was shortened to VC. For radio communication, soldiers would use the phonetic alphabet to spell VC, thus VC becomes Victor Charlie. Soldiers, as they do, then used the name Charlie to refer to the Viet Cong.