It is 74 years since the Clyde-built HMT Lancastria was bombed and sunk off the coast of France during the Second World War.
There were thought to be more than 6,000 servicemen and civilians on board, with some estimates as high as 9,000.
Only about 2,500 survived, representing a greater loss of life than the Titanic and Lusitania disasters combined.
Members of the Lancastria Association of Scotland will attend a service in Clydebank on the site of the former William Beardmore and Sons shipbuilding yard (now the Golden Jubilee National Hospital), where the Lancastria was built.
Chairwoman Fiona Symon said: "This annual commemorative service provides support for survivors, their families and the families who lost loved ones during the sinking of the Lancastria.
"It took a long time to erect a major memorial in our country to tell the story of such enormous sacrifice. However, we are grateful that the memorial is freely accessible to all at any time and hopefully will bring some comfort to so many families who have no known grave to visit in France.
"It is also fitting that the memorial is situated, not only where the Lancastria was built, but also on the site of a national hospital that helps save lives on a daily basis."
Launched as the cruise ship Tyrrhenia, the Lancastria was taken over as a troop ship in 1939.
After evacuating troops from Norway, the Lancastria headed for France to rescue many of the 150,000 troops left behind after Dunkirk.
The ship was sunk by a German bomber off the French coast at St Nazaire on June 17 1940. Four bombs were dropped at 3.50pm, sinking her within 20 minutes.
Winston Churchill banned all news coverage of the disaster, fearing the scale of the tragedy would affect public morale.