A £6m memorial to the 55,573 airmen of Bomber Command who died during World War Two is to be unveiled by the Queen.
She will be joined by royals including the Prince of Wales at the dedication ceremony in London's Green Park.
Some 6,000 veterans and families of the deceased will see a Lancaster Bomber drop 82,000 poppies in a flypast.
Britain's policy of large-scale area bombing near the end of World War II has been criticised by some, stalling progress on a memorial for decades.
Veterans from Australia, New Zealand, Canada and other countries who served alongside the British crew will also attend the ceremony.
The memorial, designed by Liam O'Connor, built in Portland stone features a bronze 9ft-high sculpture of seven aircrew.
The memorial was built after a five-year campaign
Sculptor Philip Jackson said his work was intended to be reflective and so portrayed the men after they had returned from a mission.
"I chose the moment when they get off the aircraft and they've dumped all their heavy kit onto the ground, and they're looking back and looking for their comrades."
The memorial also has a roof made from aluminium reclaimed from a Handley Page Halifax III bomber shot down over Belgium in May 1944.
An inscription says it "also commemorates those of all nations who lost their lives in the bombing of 1939-1945".
Pilot Alan Biffen, 87, said: "I am so glad that at long last Bomber Command is being remembered not only for what it achieved but also for the lives of the young men who never came back.
"Many of them were boys. I myself added a year to my age at 16 so that I could join the air force."
Almost half of the 125,000 men of Bomber Command died dodging night fighters and anti-aircraft fire in raids over occupied Europe.
No campaign medals
The ceremony is the culmination of a five-year campaign, spearheaded by the late Bee Gees singer Robin Gibb.
“It was part of the task of finishing the war and I console myself that this is what we had to do”
Bomber Command veteran
The Bomber Command Memorial Appeal secured funding from public donations and private donors John Caudwell, Lord Ashcroft and Richard Desmond.
There were no campaign medals for Bomber Command after the war and no mention of them in Churchill's victory speech.
The unit was criticised by some for raids on Dresden in the closing months of the war.
The fire-storms caused by the RAF and US Army Air Force killed about 25,000 civilians destroying the city centre.
Speaking at Green Park, Bomber Command veteran Cecil Hayley agreed the memorial was about reconciliation as well as remembrance.
"I sometimes look back in horror to think what I was required to do. But, it was what we were trying to do... it was part of the task of finishing the war and I console myself that this is what we had to do."
Bomber Command Association chairman Malcolm White said it was clear that the memorial's message included a sense of reconciliation.
"That's why its writ large on the wall -'we remember those of all countries who died in 39-45',"
He said he had been in touch with the mayor of Dresden and spoken to media in the German city as part of the project.
"Let's put it in the modern context; let's not forget the sacrifice of those who this memorial remembers," he added.
Councillor Alastair Moss defended Westminster Council's decision to grant planning permission to the memorial:
"Since our decision, this memorial has been the subject of controversy by a vocal minority who have unfortunately distracted from its significance," he said.
"We believe Westminster Council was absolutely right to grant consent for a monument which reflects what the majority of today's public want to say about bravery, sacrifice and suffering."
The event will end with a flypast by five GR4 Tornado bomber aircraft and the RAF's last flying Lancaster Bomber, which will drop the poppies over the park in remembrance for the aircrew lost.
The RAF Benevolent Fund will take over guardianship of the memorial.
History of Bomber Command
Formed in 1936
Mission to attack Germany's airbases, troops, shipping and industrial complexes connected to the war effort
Crews from UK, Canada, Australia, New Zealand and all corners of Commonwealth plus occupied nations like Poland and France and allied countries such as the US
Average age of bombers about 22
Switched to inaccurate night bombing to reduce casualties
First "thousand-bomber raid" in May 1942 - against Cologne, three months after "Bomber" Harris made commander in chief
Famous Dambusters raid of May 1943 struck at dams surrounding Ruhr Valley