By Kara Fox and Matthew Robinson, CNN

(CNN) -- Britain's Queen Elizabeth II has paid tribute on behalf of "the whole free world" to those who died during the Normandy landings in a poignant speech at D-Day commemorations in Portsmouth, southern England.

In a heartfelt speech, Elizabeth described her own wartime generation as resilient, saying that she was "delighted" to be at the event, which marked 75 years since the Allied invasion of Nazi-occupied France.

"When I attended the commemoration of the 60th anniversary of the D-Day landings, some thought it might be the last such event. But the wartime generation -- my generation -- is resilient, and I am delighted to be with you in Portsmouth today," she said.

The Queen paid homage to the hundreds of thousands of servicemen who "left these shores in the cause of freedom," and quoted a broadcast delivered by her father, King George VI at the time: "What is demanded from us all is something more than courage and endurance; we need a revival of spirit, a new unconquerable resolve."

"That is exactly what those brave men brought to the battle, as the fate of the world depended on their success," she said, thanking the veterans for their service.

"The heroism, courage and sacrifice of those who lost their lives will never be forgotten. It is with humility and pleasure, on behalf of the entire country -- indeed the whole free world -- that I say to you all, thank you," she said.

The Queen's speech was greeted with a warm round of applause, which was followed by a striking UK military flypast.

Earlier, US President Donald Trump spoke on stage, where he read a prayer that Franklin D. Roosevelt gave over the radio during the Normandy landings.

UK Prime Minister Theresa May also delivered an emotive reading of a letter by Captain Norman Skinner of the Royal Army Service Corps, who was killed the day after arriving in Normandy.

Other world leaders in attendance included German Chancellor Angela Merkel, French President Emmanuel Macron and Canada's Prime Minister Justin Trudeau, among others.

D-Day -- the military term for the first day of the Normandy landings -- was the largest amphibious invasion ever undertaken, laying the foundations for the Allied defeat of Nazi Germany in World War II.

The invasion took place on June 6, 1944, and saw of tens of thousands of troops from the United States, the UK, France, Australia and Canada landing on five stretches of the Normandy coastline.

The plan began more than a year in advance, and the Allies carried out substantial military deception -- codenamed Operation Bodyguard -- in order to confuse the Germans as to when and where the invasion would take place.

The operation was originally scheduled to begin on June 5, when a full moon and low tides were expected to coincide with good weather, but storms forced a 24-hour delay.

More than 4,400 Allied troops were confirmed dead, with at least 9,000 wounded or missing on D-Day alone.

While the exact numbers of German casualties on the day are not known, they are estimated to be between 4,000 and 9,000.