The men were convicted of kidnapping, torturing and killing leftist dissidents.
Argentina's La Nacion reported that the most prominent of the defendants, Jorge 'Tigre' Acosta, Ricardo Cavallo and Alfredo Astiz, a 59-year-old former navy spy nicknamed "the Angel of Death", were sentenced to life imprisonment for crimes committed in the Navy's School of Mechanics (ESMA).
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The ruling was reportedly read before a large crowd of political activists who clapped and cheered, according to La Nacion.
Mr Astiz is accused of participating in the disappearance, torture and murder of two French nuns, a journalist and three founders of a human rights group that he infiltrated while spying for the dictatorship.
Judges Ricardo Farias, Daniel Obligado and German Castelli delivered the sentence after nearly two years of hearings involving 160 witnesses.
