Newly released FBI documents detail a potential plot to assassinate Queen Elizabeth II during her 1983 visit to the United States.
The cache of files released on the Bureau's website, shows intelligence provided to agents about threats to the Queen on her trip.
One document details a threat reported to the FBI from a San Francisco police officer.
The officer said he received a call from a man he met at an Irish pub.
He told the officer he wanted revenge for his daughter who he said was killed in Northern Ireland by a rubber bullet.
He claimed he was going to attempt to harm the Queen and would do this "either by dropping some object off the Golden Gate Bridge onto the Royal Yacht Britannia when it sails underneath," or when she visited Yosemite National Park, the document said.
The Secret Service responded by closing the walkways to the Golden Gate Bridge, but what action they took in response to the Yosemite threat wasn't revealed, with the Queen visiting the park as scheduled.
The document noted the officer who told the FBI of the plot was "Generally cooperative although he makes no secret of his sympathies for the IRA".
The documents show many of the Queen's visits to the US in the 1980s during the Troubles in Northern Ireland were tense.
Ahead of her 1989 visit to Kentucky, an internal FBI memo said "the possibility of threats against the British Monarchy is ever-present from the Irish Republican Army".
"Boston and New York are requested to remain alert for any threats against Queen Elizabeth II on the part of IRA members and immediately furnish same to Louisville," it said.
The files were uploaded to the Vault, the FBI's information website, following a Freedom of Information Act request submitted by US media outlets.
