The Special Operations Branch (SO) was a branch of the Office of Strategic Services during World War II that "pioneered" many of the unconventional warfare, counter-insurgency (COIN), and foreign internal defense tactics and techniques used by today's US Military Special Operations Forces (SOF).

[1][3][4][5][6] The Chief of SO, Millard Preston Goodfellow, reported to the deputy director of Strategic Services Operations.

The primary objective of the Special Operations Branch is the destruction of enemy personnel, materiel, and installations."

[8] Special Operations operators and agents trained first at Camp X, then at Camp David, and several National Park Service properties around the Washington, D.C.

[9] The concept of OSS Operational Groups (OG) began as Special Operations units within SO Field Bases, but eventually outgrew the SO, where the newly established Operational Group Command was granted Branch status.