The Christian family of eight were about to be decapitated by ISIS brutes when they were attacked by special forces.
The snipers shot dead two would-be executioners who were holding knives at the throats of a father and a son who had refused to convert to Islam.
The raid came after a joint SAS and Peshmerga patrol was warned that gunmen were murdering Christian families.
It took place last July, but details of the operation emerged only last week.
The SAS had been conducting mopping up operations after the fall of Mosul when inhabitants of a Christian village told the troops that Isis were executing civilians nearby.