The Queen, the Duke of Edinburgh and other members of the Royal Family will attend the dedication and unveiling of a memorial to tens of thousands of airmen who died in the Second World War.
The Bomber Command Memorial in London's Green Park remembers the sacrifice and bravery of the 55,573 RAF crew who lost their lives in the conflict.
Its centrepiece is a 9ft bronze sculpture depicting a seven-man bomber crew returning from a mission. The design of the roof is inspired by a Vickers Wellington aircraft and incorporates sections of aluminium recovered from a Handley Page Halifax III bomber shot down over Belgium on May 12 1944, killing eight crew.
Businessman and philanthropist Lord Ashcroft, who donated the final £1 million to complete the project, has said he hopes the £7 million memorial made from Portland stone will inspire young people to read and learn about the war and the courage of those who fought in it.
The former deputy chairman of the Conservative Party said: "The whole concept of Bomber Command was bombing cities, and there were differences of opinion as to whether civilian casualties were part of a war machine.
"But those were the political decisions, and it's not for me to go into those decisions. These men were not politicians, they were carrying out their duty. And bravery is not just on the side of the Allies. I commend bravery in foreign troops, the other soldiers of a war.
"It's the concept of bravery and I think we should just focus on what these men did, being ordered to do, and did night after night in the skies over Europe."
More than 5,000 veterans and veterans' family members will attend the ceremony to mark the opening of the memorial, when it will be handed over to the RAF Benevolent Fund to maintain.
The Queen and the Duke will be met by Air Commodore Malcolm White, chairman of the Bomber Command Association. The Prince of Wales and the Duchess of Cornwall, the Duke of York, the Earl and Countess of Wessex, the Duke and Duchess of Gloucester and the Duke of Kent will also attend.
A service to dedicate the memorial will follow and the Queen will unveil the sculpture of the seven bomber air crew. There will be a flypast at the end of the service by five RAF GR4 Tornado bomber aircraft crewed by the RAF. This will be followed by a flypast by the RAF's last flying Lancaster Bomber, which will drop poppies over the park as a message of remembrance for those who died.