FBI file reveals 1983 plot to kill Queen Elizabeth II during US visit

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Britain's Queen Elizabeth II faced a potential assassination threat 40 years ago, ahead of a trip to the United States, according to newly released documents from the Federal Bureau of Investigation.

A cache of 103 pages were posted to the FBI's online records site, The Vault, on Tuesday. The files cover preparations for several trips the late Queen made to the US, including an official tour of the West Coast with her husband, Prince Philip, in 1983.

One document appears to detail a tip gathered around a month before that visit from San Francisco police regarding a phone call from "a man who claimed that his daughter had been killed in Northern Ireland by a rubber bullet."

It continues: "This man additionally claimed that he was going to attempt to harm Queen Elizabeth and would do this either by dropping some object off the Golden Gate Bridge onto the Royal Yacht Britannia when it sails underneath, or would attempt to kill Queen Elizabeth when she visited Yosemite National Park."

The same document notes that "it is the intention of the Secret Service to close the walkways on the Golden Gate Bridge when the yacht nears." There's no mention of any precautions that may have been taken at the national park nor do the files reveal whether any arrests were made.

The files illustrate the FBI's hypervigilance at possible threats to the visiting British monarch, collaboration with the US Secret Service and concerns about the Irish Republican Army (IRA) and its sympathizers during royal visits.

The Queen's cousin, Louis Mountbatten, was assassinated by the Provisional IRA in 1979, using a bomb planted in his fishing boat. Three others died in the same explosion, including two children. Many of the Queen's trips to the US took place amid the Troubles in Northern Ireland and the documents reveal the FBI was closely monitoring as it prepared for royal visits over the years.

Ahead of a private visit to Kentucky in 1989, one document notes that while the FBI was unaware of any specific threats to the Queen, "the possibility of threats against the British monarchy is everpresent from the Irish Republican Army (IRA)."

Elsewhere in the files, a document preparing for the Queen's state visit in 1991 outlines concern about Irish groups organizing protests at several scheduled engagements, including a baseball game the monarch was due to attend and a White House event. Citing information printed in a Philadelphia Irish newspaper titled Irish Edition, the page read: "The article stated anti-British feelings are running high as a result of well publicized injustices inflicted on the Birmingham Six by the corrupt English judicial system and the recent rash of brutal murders of unarmed Irish nationalists in the six counties by loyalist death squads."

It added: "Though the article contained no threats against the President or the Queen, the statements could be viewed as being inflammatory. The article stated that an Irish group had reserved a large block of grand stand tickets."

Another document in the file, dated July 1976, mentioned an occasion when the Queen traveled back across the Atlantic to help mark America's bicentennial celebrations, with stops including Philadelphia, Washington and New York.

During that trip, the FBI documents disclose, a summons was issued to a pilot for flying a small two-seater plane over Battery Park, carrying a sign that read "England, Get out of Ireland."