Queen Elizabeth II's death on Thursday ended the longest reign of any British monarch and set into motion a contingency plan known as Operation London Bridge.
Developed in the 1960s, the plans for services and succession have been periodically revised in the ensuing decades and were revealed in detail in 2019, according to The Daily Mail.
The death of the monarch in Scotland has also triggered a part of the contingency plan known as Operation Unicorn, which sets in motion additional ceremonial events in Edinburgh ahead of the logistics of moving the queen's coffin back to London.
According to the plan, the first person outside of the queen's Scottish residence Balmoral and Buckingham Palace to be informed of her death was the prime minister in a phone call.
It has been rumored since the plan was first prepared that the code "London Bridge has fallen" would be used to communicate her death, but it has not been confirmed if that took place Thursday.
According to documents seen by Politico last year, the plan spells out the process for announcing the queen's death, the official mourning period in Britain and Commonwealth countries and her funeral arrangements.
A number of institutions are set to take part in the operation, including the media, the Metropolitan Police Service, the Church of England, the British Armed Forces, Transport for London, the Royal Parks, the Greater London Authority and London boroughs.
Politico reported that in the hours after the queen's death, a series of phone calls will take place informing senior ministers and officials. Elizabeth's private secretary was chosen to spread the news of her death to the prime minister.
According to The Hill, U.K. Prime Minister Liz Truss commented shortly after the death, and other officials waited to speak until after the prime minister delivered her remarks.
The Commonwealth countries where Elizabeth served as queen will receive the news from the Foreign, Commonwealth and Development Office's Global Response Centre and the British, Scottish, Welsh and Northern Irish parliaments will convene for emergency meetings. Truss will also address the House of Commons.
Elizabeth's heir, Charles, Prince of Wales, effectively became king, though protocol dictates he will be declared the new monarch the day after her death. He will have a ceremony in a separate operation known as Operation Spring Tide.
Prince William ascended to the Duke of Cornwall and became next in the line of succession, followed by his children Prince George, Princess Charlotte and Prince Louis.
Government buildings lowered their flags to half-staff.
"There are really two things happening," one of Charles' advisers told The Guardian in 2017. "There is the demise of a sovereign, and then there is the making of a king."
The day after the queen's death, the Accession Council will recognize the new king at St. James' Palace, according to Politico.
Parliament will be suspended for 10 days and will swear allegiance to King Charles III, and the governments of Scotland, Wales and Northern Ireland will recognize the new monarch within two days after Elizabeth's death.
According to the plan, King Charles will begin a tour of the United Kingdom three days after the queen's death.
It is expected that the queen will be laid to rest on a Sunday, 10 days after her death.
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