World leaders, royalty and hundreds of veterans will honour those who fought in the D-Day landings 75 years ago during a national commemoration ceremony.

The Queen will be joined by Prime Minister Theresa May and US president Donald Trump alongside 300 veterans in Portsmouth on Wednesday to mark the forthcoming anniversary.

Some 60,000 members of the public are expected to attend the Portsmouth Naval Memorial on Southsea Common for the event which marks the 75th anniversary of the biggest amphibious invasion in military history.

READ MORE: Theresa May urges need for Western unity as she marks 75th anniversary of D-Day landings

 
D-Day 75th anniversaryFinal preparations have been made on Southsea common ahead of the D-Day 75 National Commemorative Event (Andrew Matthews/PA)

Considered a turning point in the Second World War, Operation Overlord saw thousands killed and injured after it launched on June 6 1944.

Mrs May will be making her final official appearances as the British Prime Minister during the D-Day commemorations which continue on Thursday across Normandy.

Meanwhile, hundreds of veterans are flocking to northern France and Portsmouth, as well as to events around the country, to mark the occasion.

On Wednesday Mrs May will host 15 world leaders and representatives in the Hampshire port city.

The event will be the first time the UK has hosted this many world leaders outside a formal summit since the 2012 Olympics.

READ MORE: Letters: As a D-Day veteran, I look around and think: why did we bother?

A mass security operation has been launched in the wake of Mr Trump’s attendance at the event – as part of his UK state visit.

Some critics have claimed his presence draws focus away from the veterans.

Royal British Legion D-Day anniversary voyage for veteransRoyal Marines wave Union flags as MV Boudicca arrives into Poole in Dorset (Andrew Matthews/PA)

Representatives from every country that fought alongside the UK in Operation Overlord – the Battle of Normandy – will attend commemorations as well as The Prince of Wales, members of the armed forces and the veterans who are all over 90 years old.

Joining Mrs May will also be First Minister Nicola Sturgeon, French president Emmanuel Macron, the German chancellor Angela Merkel as well as prime ministers from Canada, Australia, New Zealand, Belgium, Czech Republic, Greece, Luxembourg, The Netherlands, Norway, Poland, Slovakia and Denmark.

Mrs May is expected to describe the landings as a “moment of historic international co-operation” in which veterans fought for liberty and peace.

She will call for unity in western Europe, adding: “The global challenges we face today are different in their origin and nature. But as we confront new and evolving threats to our security it is more important than ever that we continue to stand together in upholding our shared values and way of life.

“As I host leaders from around the world today to mark this significant moment in our shared history, we will together reflect on the continued importance of the western alliance for all our countries’ security and prosperity.”

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An hour-long production telling the story of the invasion will be played to the crowds featuring testimony from veterans before theatrical performances, live music as well as a flypast of the Red Arrows and Spitfires take place.

Royal British Legion D-Day anniversary voyage for veteransStanley Elliss, 97, from Ashford, walks on a the beach at Dunkirk in France, with his daughter Susan, on the second day of a trip arranged by the Royal British Legion for D-Day veterans to mark the 75th anniversary of D-Day (Kirsty O’Connor/PA)

As part of the performance Mrs May will read a letter written by Captain Norman Skinner of the Royal Army Service Corps to his wife Gladys on 3 June 1944. The letter was in his pocket when he landed on Sword Beach on June 6 1944. He was killed the next day, leaving behind his wife and two young daughters.

Afterwards world leaders will meet to discuss the western alliance and security after a reception with veterans.

From the deck of the aircraft carrier HMS Queen Elizabeth, Mrs May and Defence Secretary Penny Mordaunt will wave off the crowds of veterans who are set to retrace the journey they made across the channel 75 years ago. This time they will be followed by a flotilla of Royal Navy vessels.

More than 4,000 personnel will be involved in D-Day events in the UK and France, in what is set to be one of the biggest mobilisations of the UK Armed Forces in recent history.

Later in the afternoon veterans Harry Read, 95, and John Hutton, 94, will parachute into Normandy in honour of comrades they lost when they first made the descent 75 years ago.

Alongside around 280 paratroopers they will take part in the jump onto fields at Sannerville – the drop zone for the 8th Midlands Parachute Battalion during D-Day.

In the evening, a vigil and silent march will take place at Pegasus Bridge which was the scene of a 15-minute skirmish to take hold of the pathways over the Caen Canal and River Orne. This was one of the first places British troops liberated on D-Day.