Do not confuse a court-martial board with a jury. There is no such thing as a jury ('twelve good men and true') in any military trial in the US, and never has been.

BTW, Calley's court-martial sentenced him to life in prison. He was (after about 4 years 'house arrest') released by a civilian court review because of alleged judicial errors. His dishonorable discharge and loss of all rank and veteran's benefits stood.