A History of the 21st Special Operations Squadron In Thailand History of the 21st Sos 1967 1975. A History of the 21st Special Operations Squadron 1967 1975 Last Revised December 16, 1998 Authors Notes First, I make every effort to be as accurate as possible. The first sections are drawn directly from my Squadron Yearbook very unusual for a unit to have one and my own bailable memories of events that