Highly-detailed plans prepared and rehearsed for decades came into effect on Thursday following the announcement of the Queen's death.
The schedule of events, commemorations and royal duties take on a series of codenames that relate to both the movements of the Queen's coffin and that of her grieving family.
King Charles III must give the plans final approval.
Operation London Bridge
The name for events between the death of the Queen and her funeral. Forth Bridge dealt with the Duke of Edinburgh’s death last year, while Menai Bridge relates to the Prince of Wales.
Operation Lion is the overarching plan for any royal death. As the Queen's death happened at her Balmoral home in Scotland, it activated Operation Unicorn, specifically for those circumstances.
Operation Spring Tide
This covers the new King’s upcoming trip around the UK and its name stems from an especially high spring tide, which is known as a “King tide”.
There are separate names for each country he will visit, expected to be in the days following a procession along the Royal Mile in Edinburgh on Monday.
King Charles III will visit Scotland (Operation Kingfisher), Wales (Operation Dragon) and Northern Ireland (Operation Shamrock).
This covers the four days of the Queen’s lying-in-state, focusing on the arrangements inside Westminster Hall.
It's expected to begin on Wednesday, September 14, ending on Sunday before her funeral the next day.
Senior royals are also expected to pay their respects once more here, standing guard in a tradition known as the Vigil of the Princes.
It is linked to Operation Feather, the arrangements for the public who are expected to queue in their thousands for an opportunity to see the monarch's coffin as they did 20 years ago for her mother.
Operation Golden Orb
Plans not only cover the immediate aftermath of the Queen's death but also look ahead to King Charles III’s future coronation.
Held at Westminster Abbey in many months’ time, it will see Camilla crowned Queen at his side.
The remarkable life of the Queen remembered in our latest episode of What You Need To Know