Kadish said he had made a mistake in sharing the confidential papers
An 85-year-old former civilian employee of the US Army has been fined for passing classified documents to Israel in the 1980s.
Ben-Ami Kadish was spared jail because of his age and health, but ordered to pay $50,000 (£31,000) by a US court.
The judge said the case was "shrouded in mystery" and he was surprised it took the FBI so long to charge Kadish.
Kadish said: "I thought I was helping the state of Israel without harming the United States."
Prosecutors said that between 1980 and 1985 Kadish provided information about nuclear weapons, fighter jets and missiles to an Israeli agent, Yosef Yagur, who photographed the documents at Kadish's residence.
"Why it took the government 23 years to charge Mr Kadish is shrouded in mystery," US District Judge William Pauley said during sentencing in Manhattan federal court.
"It is clear the (US) government could have charged Mr Kadish with far more serious crimes."
Kadish was arrested in April 2008 and pleaded guilty to being an unregistered agent of Israel in December.
Court documents showed that Yosef Yagur was also the main Israeli contact for Jonathan Pollard, an American sentenced to life in prison for spying for Israel in the 1980s.
The judge said he had given Kadish a lenient sentence, but that he had committed "a grave offence" and had "abused the trust" of the US.
Kadish told the court: "It was a mistake. It was a misjudgment."
Kadish was born in the US but grew up in Palestine before the founding of the state of Israel in 1948.