The Counterinsurgency Support Office was established on Okinawa in 1963 to supply clothing, weapons and equipment to Special Forces in Vietnam. Principally run by Ben Baker, the office issued standard and untraceable (sterile) gear (such as this ammo pouch and this rucksack).

This item is an Indigenous poncho liner, its smaller and a bit thinner than the US version. It came with a matching CISO Poncho that was a darker green.