An Argentine former navy captain on trial in Spain for genocide said he invented a story about pushing drugged political prisoners out of planes to provoke an investigation into the country's dirty war.

He had later repeated the story to journalists to boost his chances of book and movie deals, he told the court.

Adolfo Scilingo appeared alert and combative as he began his first day of evidence despite his claims he is 37 days into a hunger strike.

Scilingo told the court he pieced together bits of information he had heard during 15 years in the navy to create an elaborate tale of how suspected leftists were tortured during Argentina's 1976-1983 military dictatorship.

Among his motives, he said he wanted to provoke a wider investigation into the navy's activities during the dirty war that would reveal "a bombshell", but he did not elaborate.

Scilingo had previously admitted to investigators pushing drugged, political prisoners out of planes into the sea.

"I was very nervous during that testimony because I was speaking pure nonsense," Scilingo, 58, said of a sworn statement he gave in 1997 at the start of the Spanish investigation.

Scilingo became a naval officer during Argentine military rule from 1976 to 1983, when authorities cracked down on suspected leftists insurgents. Thousands disappeared without a trace.

"There really was terrorism," Scilingo said of the Marxist inspired groups operating at the time.

Scilingo has also told journalists in dozens of interviews that he was repentant about participating in two "death flights" in June and August of 1977 when he said 30 prisoners were stripped and shoved out of planes.

But he told the court he could not have been involved because he had been in hospital in June 1977 and on vacation in August of that year. "I never participated in any of the events," Scilingo said.

Scilingo has told investigators he prepared electrical devices used to shock prisoners during interrogations and that he saw pregnant women being held at a detention centre so that they could give birth only to have their babies stolen.

"It was a good story. The press loved it," he said.