SOG was the most secret elite U.S. military unit to serve in the war in Vietnam, so secret it was "black" - meaning its very existence was carefully concealed, even denied by the government. Innocuously code-named the Studies and Observations Group, SOG contained only volunteers from such elite units as the Army Green Berets, USAF Air Commandos, and Navy SEALs, and answered directly to the Pentagon's Joint Chiefs, with some missions requiring approval from the White House.

Inside Vietnam, only General William Westmoreland and a few senior non-SOG officers were briefed on SOG activities. Now the never-before-revealed exploits of this top-secret commando unit are vividly recounted by Major John L. Plaster, a three-tour SOG veteran.

SOG took on the most dangerous assignments, going behind enemy lines to penetrate North Vietnamese military facilities in Laos and Cambodia and along the heavily defended Ho Chi Minh Trail, where only air support - and sometimes no support at all - was available.