King Charles' Coronation will see snipers on rooftops and the use of anti-drone technology amid concerns terrorists or protestors could target next week's event.
Thousands of police officers will be deployed to London's streets on May 6 as part of a huge security operation - dubbed Operation Tower of London - to guard the Crown Jewels from any potential thieves.
They will be backed up by elite teams of armed guards, snipers and the military.
Counter-drone radar units will also be set up along the King and Queen's procession route, as well as devices to block signals between pilots on the ground and their aircraft.
The Civil Aviation Authority has imposed a “no-fly zone” over Central London, banning aircraft from flying below various altitudes in certain areas on the afternoon.
A source told the Mirror: "The operation is huge, certainly in a similar scale to that of the funeral of the Queen, the largest event in a generation.
"Every available arm of the police and security services has been dispatched.
"The exercise turns the Abbey into Operation Tower of London, focusing on maximum security and maximum lockdown."
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The top-secret operation comes after reports that specialist cops had widened their remit from concentrating on established terror groups and other “fixated individuals”, to controversially include members of peaceful campaign groups.
Graham Smith, Republic's chief executive, previously said activists will wear yellow T-shirts and carry yellow placards in groups along the procession route.
He vowed to make the peaceful demonstration unmissable and loud, but said they were not staging any Extinction Rebellion-style stunts because "it's not a good look" and "doesn't help the cause".
More than 1,350 people had pledged to take part as of mid-April, he added.
Mr Smith told The Times: "Anti-monarchy protests will carry one simple message: Do you want Charles or do you want a choice?"
He also branded the crowning of Charles and the Queen Consort a "pointless piece of theatre" which will cost tens of millions of pounds and be a "slap in the face" for people struggling with the cost-of-living crisis.
Protesters have already targeted Charles at recent public appearances, with their "Not my King" signs and shouts of "Why are you wasting money on a Coronation Charles?".
The group is asking people to sign a pledge to protest and to add their voices to their call for the UK to become a republic and have an elected head of state.
"On Saturday 6th May the eyes of the world will be on the coronation," its website says. "This is the moment we make our objection loud, visible and impossible to ignore."
The campaigners have written to every police force in the UK including the Metropolitan Police asking for reassurances they will not interfere in "peaceful and meaningful" protests against the monarchy.
A YouGov survey carried out earlier this month found that 51% of adults questioned believe the ceremony should not be funded by the Government.
Almost a third – 32% – said it should, while around 18% did not know.
In relation to communication with Republic, a spokesperson for the Met Police previously said: "We always seek proactive engagement with protest groups to understand what their intention is, and how we can work with them."
