The Queen joined 2,000 people at Westminster Abbey to mark the 90th anniversary of the Gallipoli landings.
The Queen departs Westminster Abbey after the service
More than 100,000 soldiers, including 21,000 British and Irish, died during the eight-month World War I campaign.
Prince Charles visited the landing spot in Turkey - which had been aligned with Germany and suffered most of the mission's fatalities - on Anzac Day.
The mission's aim was to push through the Dardanelles straits and capture the Turkish capital.
Many Australians and New Zealanders were among those gathered at Westminster Abbey to offer their respects.
Dean of Westminster Wesley Carr told the congregation: "There is now no one left who fought in that landing.
"We remembered the last two soldiers, two from each country, a few years ago.
"But the memory of that war is with us as a warning and as an encouragement.
"We are warned that any war involves not just grand strategies but the deaths and suffering of ordinary men and women."
Songs were sung in Maori and readings were given by the Australian High Commissioner Richard Alston and Turkish Ambassador Akin Alptuna.
Prince Charles represented the Queen - who was accompanied by the Duke of Edinburgh in London - during a dawn service at Anzac Cove, the scene of the landings on 25 April 25, 1915.
The Gallipoli campaign went down in history as a costly failure.