The "death flights" were among the more macabre innovations of Argentina's 1976-1983 dictatorship.
The military planes that flew out over the wide Rio de la Plata and back returned missing many of their passengers: political prisoners who were drugged to sleep and thrown alive into the sea.
A group of pilots who allegedly flew the missions are among the 68 suspects who went on trial Wednesday, charged with participating in hundreds of kidnappings, tortures and murders inside Argentina's Naval Mechanics School.
The leafy campus, which is now a human rights museum, served as a huge clandestine prison during the junta's campaign to eliminate leftist subversives. More than 5,000 political prisoners were processed there, the vast majority of them made to disappear.
The new trial is the third involving the school, and the biggest yet, involving a total of 789 victims.
The suspects include some dictatorship-era officials who have already been convicted and are serving life terms, such as former Capt. Alfredo Astiz, known as the "Angel of Death" for his work delivering dissidents to the junta as an undercover agent.
The pilots include Julio Poch, who was extradited from Spain after a long career flying commercial jets in Europe; retired coast guard officers Enrique Jose De Saint y Georges Mario Daniel Arru, who both flew for Aerolineas Argentinas after the dictatorship; and retired navy aviator Emir Sisul Hess.
Hess's former employees testified that he bragged the prisoners "fell like ants" from the planes. Poch's former coworkers said he too bragged about the flights, and dismissed the prisoners as "leftist terrorists" who deserved to die. Both men have formally denied participating in the flights.
Other human rights trials have focused on former military and police officials, but this one also includes civilians.
Juan Alemann, who was Argentina's treasury secretary during the dictatorship, is accused of participating in a torture session. Attorney Gonzalo Torres de Tolosa allegedly joined a death flight.
Rights activists long suspected that navy planes were used to dispose of bodies piling up at the Mechanics School after corpses began washing up along the coast of Argentina and Uruguay. But their big break in the case came in 1995, when former Capt. Adolfo Scilingo publicly confessed to throwing 30 victims into the sea during two flights. He was eventually sentenced to more than 1,000 years in prison.